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 $66.36   5.178%   $69.7961   $69.80   $69.80   $69.80  
  Purchase #2 $109.42   10.629%   $121.0503   $121.05   $121.05   $121.10  
  Purchase #3 $124.59   6.421%   $132.5899   $132.59   $132.60   $132.60  
  Purchase #4 $103.63   12.275%   $116.3506   $116.35   $116.35   $116.40  
  Purchase #5 $197.26   11.798%   $220.5327   $220.53   $220.55   $220.50  
  Purchase #6 $247.89   11.338%   $275.9958   $276.00   $276.00   $276.00  
  Purchase #7 $84.41   12.741%   $95.1647   $95.16   $95.15   $95.20  
  7 purchase totals = $933.56       $1,031.4801   $1,031.48   $1,031.50   $1,031.60