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 $164.49   7.805%   $177.3284   $177.33   $177.35   $177.30  
  Purchase #2 $236.73   4.557%   $247.5178   $247.52   $247.50   $247.50  
  Purchase #3 $84.86   10.746%   $93.9791   $93.98   $94.00   $94.00  
  Purchase #4 $201.48   12.169%   $225.9981   $226.00   $226.00   $226.00  
  Purchase #5 $146.91   5.843%   $155.494   $155.49   $155.50   $155.50  
  Purchase #6 $18.25   11.755%   $20.3953   $20.40   $20.40   $20.40  
  Purchase #7 $119.63   11.823%   $133.7739   $133.77   $133.75   $133.80  
  7 purchase totals = $972.35       $1,054.4866   $1,054.49   $1,054.50   $1,054.50