Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $144.60   13.274%   $163.7942   $163.79   $163.80   $163.80  
  Purchase #2 $159.78   12.636%   $179.9698   $179.97   $179.95   $180.00  
  Purchase #3 $246.71   12.547%   $277.6647   $277.66   $277.65   $277.70  
  Purchase #4 $167.95   8.412%   $182.078   $182.08   $182.10   $182.10  
  Purchase #5 $210.99   13.313%   $239.0791   $239.08   $239.10   $239.10  
  Purchase #6 $106.50   8.454%   $115.5035   $115.50   $115.50   $115.50  
  Purchase #7 $236.56   7.116%   $253.3936   $253.39   $253.40   $253.40  
  7 purchase totals = $1,273.09       $1,411.4829   $1,411.47   $1,411.50   $1,411.60