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 $68.81   11.860%   $76.9709   $76.97   $76.95   $77.00  
  Purchase #2 $150.59   13.272%   $170.5763   $170.58   $170.60   $170.60  
  Purchase #3 $73.70   3.591%   $76.3466   $76.35   $76.35   $76.30  
  Purchase #4 $210.97   5.570%   $222.721   $222.72   $222.70   $222.70  
  Purchase #5 $35.38   13.187%   $40.0456   $40.05   $40.05   $40.00  
  Purchase #6 $154.33   3.819%   $160.2239   $160.22   $160.20   $160.20  
  Purchase #7 $21.48   12.201%   $24.1008   $24.10   $24.10   $24.10  
  7 purchase totals = $715.26       $770.9851   $770.99   $770.95   $770.90