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 $194.65   4.433%   $203.2788   $203.28   $203.30   $203.30  
  Purchase #2 $178.77   6.154%   $189.7715   $189.77   $189.75   $189.80  
  Purchase #3 $134.26   13.156%   $151.9232   $151.92   $151.90   $151.90  
  Purchase #4 $96.73   7.847%   $104.3204   $104.32   $104.30   $104.30  
  Purchase #5 $118.31   11.806%   $132.2777   $132.28   $132.30   $132.30  
  Purchase #6 $133.41   6.165%   $141.6347   $141.63   $141.65   $141.60  
  Purchase #7 $25.69   4.392%   $26.8183   $26.82   $26.80   $26.80  
  7 purchase totals = $881.82       $950.0246   $950.02   $950.00   $950.00