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 $179.39   11.273%   $199.6126   $199.61   $199.60   $199.60  
  Purchase #2 $94.75   12.593%   $106.6819   $106.68   $106.70   $106.70  
  Purchase #3 $210.94   7.437%   $226.6276   $226.63   $226.65   $226.60  
  Purchase #4 $246.61   6.871%   $263.5546   $263.55   $263.55   $263.60  
  Purchase #5 $90.36   13.400%   $102.4682   $102.47   $102.45   $102.50  
  Purchase #6 $69.56   7.723%   $74.9321   $74.93   $74.95   $74.90  
  Purchase #7 $180.99   6.154%   $192.1281   $192.13   $192.15   $192.10  
  7 purchase totals = $1,072.60       $1,166.0051   $1,166.00   $1,166.05   $1,166.00