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 $59.55   5.305%   $62.7091   $62.71   $62.70   $62.70  
  Purchase #2 $139.80   11.539%   $155.9315   $155.93   $155.95   $155.90  
  Purchase #3 $187.55   13.551%   $212.9649   $212.96   $212.95   $213.00  
  Purchase #4 $13.53   4.819%   $14.182   $14.18   $14.20   $14.20  
  Purchase #5 $11.35   5.774%   $12.0053   $12.01   $12.00   $12.00  
  Purchase #6 $108.42   11.686%   $121.09   $121.09   $121.10   $121.10  
  Purchase #7 $26.40   3.595%   $27.3491   $27.35   $27.35   $27.30  
  7 purchase totals = $546.60       $606.2319   $606.23   $606.25   $606.20