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 $236.29   4.685%   $247.3602   $247.36   $247.35   $247.40  
  Purchase #2 $54.68   3.711%   $56.7092   $56.71   $56.70   $56.70  
  Purchase #3 $5.62   7.108%   $6.0195   $6.02   $6.00   $6.00  
  Purchase #4 $41.46   9.434%   $45.3713   $45.37   $45.35   $45.40  
  Purchase #5 $212.77   13.491%   $241.4748   $241.47   $241.45   $241.50  
  Purchase #6 $150.37   3.739%   $155.9923   $155.99   $156.00   $156.00  
  Purchase #7 $104.43   11.714%   $116.6629   $116.66   $116.65   $116.70  
  7 purchase totals = $805.62       $869.5902   $869.58   $869.50   $869.70