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 $119.54   11.450%   $133.2273   $133.23   $133.25   $133.20  
  Purchase #2 $122.46   13.266%   $138.7055   $138.71   $138.70   $138.70  
  Purchase #3 $85.42   8.855%   $92.9839   $92.98   $93.00   $93.00  
  Purchase #4 $31.53   6.788%   $33.6703   $33.67   $33.65   $33.70  
  Purchase #5 $237.27   10.196%   $261.462   $261.46   $261.45   $261.50  
  Purchase #6 $233.71   6.743%   $249.4691   $249.47   $249.45   $249.50  
  Purchase #7 $172.87   5.582%   $182.5196   $182.52   $182.50   $182.50  
  7 purchase totals = $1,002.80       $1,092.0377   $1,092.04   $1,092.00   $1,092.10