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 $121.92   8.821%   $132.6746   $132.67   $132.65   $132.70  
  Purchase #2 $127.94   3.672%   $132.638   $132.64   $132.65   $132.60  
  Purchase #3 $107.65   8.614%   $116.923   $116.92   $116.90   $116.90  
  Purchase #4 $216.70   10.359%   $239.148   $239.15   $239.15   $239.10  
  Purchase #5 $53.73   5.375%   $56.618   $56.62   $56.60   $56.60  
  Purchase #6 $162.59   13.252%   $184.1364   $184.14   $184.15   $184.10  
  Purchase #7 $153.45   5.405%   $161.744   $161.74   $161.75   $161.70  
  7 purchase totals = $943.98       $1,023.8820   $1,023.88   $1,023.85   $1,023.70