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 $179.46   11.750%   $200.5466   $200.55   $200.55   $200.50  
  Purchase #2 $66.80   4.481%   $69.7933   $69.79   $69.80   $69.80  
  Purchase #3 $115.84   4.713%   $121.2995   $121.30   $121.30   $121.30  
  Purchase #4 $62.73   10.695%   $69.439   $69.44   $69.45   $69.40  
  Purchase #5 $220.53   5.112%   $231.8035   $231.80   $231.80   $231.80  
  Purchase #6 $68.30   11.770%   $76.3389   $76.34   $76.35   $76.30  
  Purchase #7 $232.40   8.868%   $253.0092   $253.01   $253.00   $253.00  
  7 purchase totals = $946.06       $1,022.2300   $1,022.23   $1,022.25   $1,022.10