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 $153.52   6.541%   $163.5617   $163.56   $163.55   $163.60  
  Purchase #2 $92.95   3.245%   $95.9662   $95.97   $95.95   $96.00  
  Purchase #3 $232.79   10.676%   $257.6427   $257.64   $257.65   $257.60  
  Purchase #4 $158.53   13.229%   $179.5019   $179.50   $179.50   $179.50  
  Purchase #5 $248.45   11.499%   $277.0193   $277.02   $277.00   $277.00  
  Purchase #6 $216.95   10.166%   $239.0051   $239.01   $239.00   $239.00  
  Purchase #7 $229.42   3.345%   $237.0941   $237.09   $237.10   $237.10  
  7 purchase totals = $1,332.61       $1,449.7910   $1,449.79   $1,449.75   $1,449.80