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 $44.86   4.294%   $46.7863   $46.79   $46.80   $46.80  
  Purchase #2 $75.70   10.387%   $83.563   $83.56   $83.55   $83.60  
  Purchase #3 $246.81   7.468%   $265.2418   $265.24   $265.25   $265.20  
  Purchase #4 $57.75   6.295%   $61.3854   $61.39   $61.40   $61.40  
  Purchase #5 $101.53   8.313%   $109.9702   $109.97   $109.95   $110.00  
  Purchase #6 $243.87   11.566%   $272.076   $272.08   $272.10   $272.10  
  Purchase #7 $97.91   9.494%   $107.2056   $107.21   $107.20   $107.20  
  7 purchase totals = $868.43       $946.2283   $946.24   $946.25   $946.30