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 $64.88   5.840%   $68.669   $68.67   $68.65   $68.70  
  Purchase #2 $149.76   13.262%   $169.6212   $169.62   $169.60   $169.60  
  Purchase #3 $155.32   12.241%   $174.3327   $174.33   $174.35   $174.30  
  Purchase #4 $115.59   9.152%   $126.1688   $126.17   $126.15   $126.20  
  Purchase #5 $58.31   4.550%   $60.9631   $60.96   $60.95   $61.00  
  Purchase #6 $115.34   9.519%   $126.3192   $126.32   $126.30   $126.30  
  Purchase #7 $72.76   4.214%   $75.8261   $75.83   $75.85   $75.80  
  7 purchase totals = $731.96       $801.9001   $801.90   $801.85   $801.90