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 $48.34   12.870%   $54.5614   $54.56   $54.55   $54.60  
  Purchase #2 $111.88   13.483%   $126.9648   $126.96   $126.95   $127.00  
  Purchase #3 $82.31   3.257%   $84.9908   $84.99   $85.00   $85.00  
  Purchase #4 $24.67   13.147%   $27.9134   $27.91   $27.90   $27.90  
  Purchase #5 $189.52   12.205%   $212.6509   $212.65   $212.65   $212.70  
  Purchase #6 $125.91   11.152%   $139.9515   $139.95   $139.95   $140.00  
  Purchase #7 $22.81   9.211%   $24.911   $24.91   $24.90   $24.90  
  7 purchase totals = $605.44       $671.9438   $671.93   $671.90   $672.10