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 $68.96   5.394%   $72.6797   $72.68   $72.70   $72.70  
  Purchase #2 $52.68   11.460%   $58.7171   $58.72   $58.70   $58.70  
  Purchase #3 $241.40   5.385%   $254.3994   $254.40   $254.40   $254.40  
  Purchase #4 $155.67   6.286%   $165.4554   $165.46   $165.45   $165.50  
  Purchase #5 $156.32   12.503%   $175.8647   $175.86   $175.85   $175.90  
  Purchase #6 $119.50   9.201%   $130.4952   $130.50   $130.50   $130.50  
  Purchase #7 $157.54   8.370%   $170.7261   $170.73   $170.75   $170.70  
  7 purchase totals = $952.07       $1,028.3376   $1,028.35   $1,028.35   $1,028.40