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 $59.58   11.483%   $66.4216   $66.42   $66.40   $66.40  
  Purchase #2 $103.30   6.165%   $109.6684   $109.67   $109.65   $109.70  
  Purchase #3 $244.86   7.812%   $263.9885   $263.99   $264.00   $264.00  
  Purchase #4 $227.34   3.618%   $235.5652   $235.57   $235.55   $235.60  
  Purchase #5 $182.38   3.630%   $189.0004   $189.00   $189.00   $189.00  
  Purchase #6 $16.30   6.393%   $17.3421   $17.34   $17.35   $17.30  
  Purchase #7 $65.60   8.423%   $71.1255   $71.13   $71.15   $71.10  
  7 purchase totals = $899.36       $953.1117   $953.12   $953.10   $953.10