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 $67.93   12.484%   $76.4104   $76.41   $76.40   $76.40  
  Purchase #2 $108.33   10.159%   $119.3352   $119.34   $119.35   $119.30  
  Purchase #3 $243.25   12.819%   $274.4322   $274.43   $274.45   $274.40  
  Purchase #4 $240.92   9.514%   $263.8411   $263.84   $263.85   $263.80  
  Purchase #5 $38.91   7.868%   $41.9714   $41.97   $41.95   $42.00  
  Purchase #6 $60.37   8.136%   $65.2817   $65.28   $65.30   $65.30  
  Purchase #7 $249.34   4.697%   $261.0515   $261.05   $261.05   $261.10  
  7 purchase totals = $1,009.05       $1,102.3235   $1,102.32   $1,102.35   $1,102.30