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 $60.55   12.390%   $68.0521   $68.05   $68.05   $68.10  
  Purchase #2 $201.52   9.646%   $220.9586   $220.96   $220.95   $221.00  
  Purchase #3 $153.33   11.307%   $170.667   $170.67   $170.65   $170.70  
  Purchase #4 $161.88   11.411%   $180.3521   $180.35   $180.35   $180.40  
  Purchase #5 $38.99   13.831%   $44.3827   $44.38   $44.40   $44.40  
  Purchase #6 $101.65   13.555%   $115.4287   $115.43   $115.45   $115.40  
  Purchase #7 $61.46   4.357%   $64.1378   $64.14   $64.15   $64.10  
  7 purchase totals = $779.38       $863.9790   $863.98   $864.00   $864.10