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 $243.61   7.460%   $261.7833   $261.78   $261.80   $261.80  
  Purchase #2 $9.54   13.741%   $10.8509   $10.85   $10.85   $10.90  
  Purchase #3 $221.28   5.735%   $233.9704   $233.97   $233.95   $234.00  
  Purchase #4 $224.33   10.323%   $247.4876   $247.49   $247.50   $247.50  
  Purchase #5 $92.73   13.159%   $104.9323   $104.93   $104.95   $104.90  
  Purchase #6 $92.99   11.323%   $103.5193   $103.52   $103.50   $103.50  
  Purchase #7 $93.62   4.291%   $97.6372   $97.64   $97.65   $97.60  
  7 purchase totals = $978.10       $1,060.1810   $1,060.18   $1,060.20   $1,060.20