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 $132.42   5.496%   $139.6978   $139.70   $139.70   $139.70  
  Purchase #2 $125.88   6.719%   $134.3379   $134.34   $134.35   $134.30  
  Purchase #3 $119.92   11.394%   $133.5837   $133.58   $133.60   $133.60  
  Purchase #4 $95.69   7.304%   $102.6792   $102.68   $102.70   $102.70  
  Purchase #5 $102.93   6.688%   $109.814   $109.81   $109.80   $109.80  
  Purchase #6 $58.42   13.715%   $66.4323   $66.43   $66.45   $66.40  
  Purchase #7 $239.51   6.320%   $254.647   $254.65   $254.65   $254.60  
  7 purchase totals = $874.77       $941.1919   $941.19   $941.25   $941.10