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 $153.50   10.721%   $169.9567   $169.96   $169.95   $170.00  
  Purchase #2 $168.92   4.375%   $176.3103   $176.31   $176.30   $176.30  
  Purchase #3 $5.34   12.723%   $6.0194   $6.02   $6.00   $6.00  
  Purchase #4 $176.41   3.209%   $182.071   $182.07   $182.05   $182.10  
  Purchase #5 $96.75   7.537%   $104.042   $104.04   $104.05   $104.00  
  Purchase #6 $95.81   5.254%   $100.8439   $100.84   $100.85   $100.80  
  Purchase #7 $214.69   3.529%   $222.2664   $222.27   $222.25   $222.30  
  7 purchase totals = $911.42       $961.5097   $961.51   $961.45   $961.50