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 $58.96   11.836%   $65.9385   $65.94   $65.95   $65.90  
  Purchase #2 $34.45   7.572%   $37.0586   $37.06   $37.05   $37.10  
  Purchase #3 $78.85   9.704%   $86.5016   $86.50   $86.50   $86.50  
  Purchase #4 $37.50   11.569%   $41.8384   $41.84   $41.85   $41.80  
  Purchase #5 $53.73   8.267%   $58.1719   $58.17   $58.15   $58.20  
  Purchase #6 $85.72   10.613%   $94.8175   $94.82   $94.80   $94.80  
  Purchase #7 $23.37   6.827%   $24.9655   $24.97   $24.95   $25.00  
  7 purchase totals = $372.58       $409.2920   $409.30   $409.25   $409.30