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 $226.83   6.527%   $241.6352   $241.64   $241.65   $241.60  
  Purchase #2 $103.71   13.216%   $117.4163   $117.42   $117.40   $117.40  
  Purchase #3 $54.85   4.695%   $57.4252   $57.43   $57.45   $57.40  
  Purchase #4 $26.49   8.519%   $28.7467   $28.75   $28.75   $28.70  
  Purchase #5 $205.81   6.591%   $219.3749   $219.37   $219.35   $219.40  
  Purchase #6 $64.39   9.589%   $70.5644   $70.56   $70.55   $70.60  
  Purchase #7 $193.45   11.712%   $216.1069   $216.11   $216.10   $216.10  
  7 purchase totals = $875.53       $951.2696   $951.28   $951.25   $951.20