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 $231.61   12.413%   $260.3597   $260.36   $260.35   $260.40  
  Purchase #2 $180.49   11.571%   $201.3745   $201.37   $201.35   $201.40  
  Purchase #3 $101.36   8.527%   $110.003   $110.00   $110.00   $110.00  
  Purchase #4 $236.81   6.567%   $252.3613   $252.36   $252.35   $252.40  
  Purchase #5 $222.65   5.817%   $235.6016   $235.60   $235.60   $235.60  
  Purchase #6 $152.28   9.793%   $167.1928   $167.19   $167.20   $167.20  
  Purchase #7 $236.74   13.341%   $268.3235   $268.32   $268.30   $268.30  
  7 purchase totals = $1,361.94       $1,495.2164   $1,495.20   $1,495.15   $1,495.30