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 $246.80   10.137%   $271.8181   $271.82   $271.80   $271.80  
  Purchase #2 $173.28   5.254%   $182.3841   $182.38   $182.40   $182.40  
  Purchase #3 $10.77   11.717%   $12.0319   $12.03   $12.05   $12.00  
  Purchase #4 $14.59   10.815%   $16.1679   $16.17   $16.15   $16.20  
  Purchase #5 $170.51   3.563%   $176.5853   $176.59   $176.60   $176.60  
  Purchase #6 $224.52   9.716%   $246.3344   $246.33   $246.35   $246.30  
  Purchase #7 $60.93   13.718%   $69.2884   $69.29   $69.30   $69.30  
  7 purchase totals = $901.40       $974.6101   $974.61   $974.65   $974.60