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 $95.69   5.629%   $101.0764   $101.08   $101.10   $101.10  
  Purchase #2 $239.78   5.857%   $253.8239   $253.82   $253.80   $253.80  
  Purchase #3 $60.29   13.821%   $68.6227   $68.62   $68.60   $68.60  
  Purchase #4 $240.51   4.710%   $251.838   $251.84   $251.85   $251.80  
  Purchase #5 $232.27   11.639%   $259.3039   $259.30   $259.30   $259.30  
  Purchase #6 $233.56   9.126%   $254.8747   $254.87   $254.85   $254.90  
  Purchase #7 $85.34   12.195%   $95.7472   $95.75   $95.75   $95.70  
  7 purchase totals = $1,187.44       $1,285.2868   $1,285.28   $1,285.25   $1,285.20