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 $36.88   13.395%   $41.8201   $41.82   $41.80   $41.80  
  Purchase #2 $64.42   4.694%   $67.4439   $67.44   $67.45   $67.40  
  Purchase #3 $112.42   6.623%   $119.8656   $119.87   $119.85   $119.90  
  Purchase #4 $199.52   7.138%   $213.7617   $213.76   $213.75   $213.80  
  Purchase #5 $57.71   9.708%   $63.3125   $63.31   $63.30   $63.30  
  Purchase #6 $74.90   10.816%   $83.0012   $83.00   $83.00   $83.00  
  Purchase #7 $157.59   9.238%   $172.1482   $172.15   $172.15   $172.10  
  7 purchase totals = $703.44       $761.3532   $761.35   $761.30   $761.30