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 $26.69   6.224%   $28.3512   $28.35   $28.35   $28.40  
  Purchase #2 $241.36   6.252%   $256.4498   $256.45   $256.45   $256.40  
  Purchase #3 $161.32   6.330%   $171.5316   $171.53   $171.55   $171.50  
  Purchase #4 $110.75   9.560%   $121.3377   $121.34   $121.35   $121.30  
  Purchase #5 $63.43   11.815%   $70.9243   $70.92   $70.90   $70.90  
  Purchase #6 $154.60   7.870%   $166.767   $166.77   $166.75   $166.80  
  Purchase #7 $27.38   5.853%   $28.9826   $28.98   $29.00   $29.00  
  7 purchase totals = $785.53       $844.3442   $844.34   $844.35   $844.30