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 $54.37   13.402%   $61.6567   $61.66   $61.65   $61.70  
  Purchase #2 $141.52   13.152%   $160.1327   $160.13   $160.15   $160.10  
  Purchase #3 $29.68   12.532%   $33.3995   $33.40   $33.40   $33.40  
  Purchase #4 $27.77   12.179%   $31.1521   $31.15   $31.15   $31.20  
  Purchase #5 $113.61   10.657%   $125.7174   $125.72   $125.70   $125.70  
  Purchase #6 $139.74   11.427%   $155.7081   $155.71   $155.70   $155.70  
  Purchase #7 $169.36   9.236%   $185.0021   $185.00   $185.00   $185.00  
  7 purchase totals = $676.05       $752.7686   $752.77   $752.75   $752.80