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 $63.82   7.230%   $68.4342   $68.43   $68.45   $68.40  
  Purchase #2 $146.57   13.554%   $166.4361   $166.44   $166.45   $166.40  
  Purchase #3 $56.35   9.231%   $61.5517   $61.55   $61.55   $61.60  
  Purchase #4 $244.66   12.311%   $274.7801   $274.78   $274.80   $274.80  
  Purchase #5 $48.32   11.700%   $53.9734   $53.97   $53.95   $54.00  
  Purchase #6 $174.30   10.585%   $192.7497   $192.75   $192.75   $192.70  
  Purchase #7 $247.93   6.604%   $264.3033   $264.30   $264.30   $264.30  
  7 purchase totals = $981.95       $1,082.2285   $1,082.22   $1,082.25   $1,082.20