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 $202.90   10.431%   $224.0645   $224.06   $224.05   $224.10  
  Purchase #2 $92.98   11.153%   $103.3501   $103.35   $103.35   $103.40  
  Purchase #3 $31.49   8.491%   $34.1638   $34.16   $34.15   $34.20  
  Purchase #4 $242.94   10.869%   $269.3451   $269.35   $269.35   $269.30  
  Purchase #5 $36.82   9.474%   $40.3083   $40.31   $40.30   $40.30  
  Purchase #6 $178.34   7.280%   $191.3232   $191.32   $191.30   $191.30  
  Purchase #7 $17.27   9.823%   $18.9664   $18.97   $18.95   $19.00  
  7 purchase totals = $802.74       $881.5214   $881.52   $881.45   $881.60