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 $191.54   11.137%   $212.8718   $212.87   $212.85   $212.90  
  Purchase #2 $37.84   5.149%   $39.7884   $39.79   $39.80   $39.80  
  Purchase #3 $210.39   6.125%   $223.2764   $223.28   $223.30   $223.30  
  Purchase #4 $122.61   6.203%   $130.2155   $130.22   $130.20   $130.20  
  Purchase #5 $219.28   6.804%   $234.1998   $234.20   $234.20   $234.20  
  Purchase #6 $230.59   13.355%   $261.3853   $261.39   $261.40   $261.40  
  Purchase #7 $86.32   6.550%   $91.974   $91.97   $91.95   $92.00  
  7 purchase totals = $1,098.57       $1,193.7112   $1,193.72   $1,193.70   $1,193.80