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 $233.92   8.825%   $254.5634   $254.56   $254.55   $254.60  
  Purchase #2 $169.96   10.760%   $188.2477   $188.25   $188.25   $188.20  
  Purchase #3 $68.71   9.731%   $75.3962   $75.40   $75.40   $75.40  
  Purchase #4 $101.69   8.749%   $110.5869   $110.59   $110.60   $110.60  
  Purchase #5 $238.65   5.688%   $252.2244   $252.22   $252.20   $252.20  
  Purchase #6 $23.98   12.608%   $27.0034   $27.00   $27.00   $27.00  
  Purchase #7 $104.91   10.705%   $116.1406   $116.14   $116.15   $116.10  
  7 purchase totals = $941.82       $1,024.1626   $1,024.16   $1,024.15   $1,024.10