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 $174.38   13.733%   $198.3276   $198.33   $198.35   $198.30  
  Purchase #2 $244.81   5.501%   $258.277   $258.28   $258.30   $258.30  
  Purchase #3 $14.25   4.732%   $14.9243   $14.92   $14.90   $14.90  
  Purchase #4 $191.95   10.546%   $212.193   $212.19   $212.20   $212.20  
  Purchase #5 $49.32   12.341%   $55.4066   $55.41   $55.40   $55.40  
  Purchase #6 $230.53   5.781%   $243.8569   $243.86   $243.85   $243.90  
  Purchase #7 $90.52   4.129%   $94.2576   $94.26   $94.25   $94.30  
  7 purchase totals = $995.76       $1,077.2430   $1,077.25   $1,077.25   $1,077.30