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 $84.52   11.210%   $93.9947   $93.99   $94.00   $94.00  
  Purchase #2 $106.72   8.486%   $115.7763   $115.78   $115.80   $115.80  
  Purchase #3 $119.31   4.137%   $124.2459   $124.25   $124.25   $124.20  
  Purchase #4 $8.42   3.827%   $8.7422   $8.74   $8.75   $8.70  
  Purchase #5 $58.34   6.773%   $62.2914   $62.29   $62.30   $62.30  
  Purchase #6 $8.99   13.289%   $10.1847   $10.18   $10.20   $10.20  
  Purchase #7 $36.91   7.762%   $39.775   $39.78   $39.80   $39.80  
  7 purchase totals = $423.21       $455.0102   $455.01   $455.10   $455.00