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 $66.51   11.551%   $74.1926   $74.19   $74.20   $74.20  
  Purchase #2 $92.61   7.139%   $99.2214   $99.22   $99.20   $99.20  
  Purchase #3 $151.28   12.292%   $169.8753   $169.88   $169.90   $169.90  
  Purchase #4 $205.56   5.366%   $216.5903   $216.59   $216.60   $216.60  
  Purchase #5 $163.33   5.414%   $172.1727   $172.17   $172.15   $172.20  
  Purchase #6 $20.98   4.208%   $21.8628   $21.86   $21.85   $21.90  
  Purchase #7 $8.48   9.185%   $9.2589   $9.26   $9.25   $9.30  
  7 purchase totals = $708.75       $763.1740   $763.17   $763.15   $763.30