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 $169.49   12.112%   $190.0186   $190.02   $190.00   $190.00  
  Purchase #2 $61.57   8.251%   $66.6501   $66.65   $66.65   $66.70  
  Purchase #3 $28.34   3.369%   $29.2948   $29.29   $29.30   $29.30  
  Purchase #4 $178.78   8.698%   $194.3303   $194.33   $194.35   $194.30  
  Purchase #5 $40.28   8.593%   $43.7413   $43.74   $43.75   $43.70  
  Purchase #6 $56.85   5.649%   $60.0615   $60.06   $60.05   $60.10  
  Purchase #7 $195.31   11.561%   $217.8898   $217.89   $217.90   $217.90  
  7 purchase totals = $730.62       $801.9864   $801.98   $802.00   $802.00