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 $218.56   12.843%   $246.6297   $246.63   $246.65   $246.60  
  Purchase #2 $204.47   12.144%   $229.3008   $229.30   $229.30   $229.30  
  Purchase #3 $119.55   12.701%   $134.734   $134.73   $134.75   $134.70  
  Purchase #4 $25.87   6.139%   $27.4582   $27.46   $27.45   $27.50  
  Purchase #5 $90.95   7.467%   $97.7412   $97.74   $97.75   $97.70  
  Purchase #6 $47.34   12.216%   $53.1231   $53.12   $53.10   $53.10  
  Purchase #7 $191.58   3.253%   $197.8121   $197.81   $197.80   $197.80  
  7 purchase totals = $898.32       $986.7991   $986.79   $986.80   $986.70