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 $101.72   9.814%   $111.7028   $111.70   $111.70   $111.70  
  Purchase #2 $231.99   5.147%   $243.9305   $243.93   $243.95   $243.90  
  Purchase #3 $62.56   5.188%   $65.8056   $65.81   $65.80   $65.80  
  Purchase #4 $136.47   9.509%   $149.4469   $149.45   $149.45   $149.40  
  Purchase #5 $19.51   11.677%   $21.7882   $21.79   $21.80   $21.80  
  Purchase #6 $247.53   9.588%   $271.2632   $271.26   $271.25   $271.30  
  Purchase #7 $131.27   13.800%   $149.3853   $149.39   $149.40   $149.40  
  7 purchase totals = $931.05       $1,013.3225   $1,013.33   $1,013.35   $1,013.30