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 $103.85   12.289%   $116.6121   $116.61   $116.60   $116.60  
  Purchase #2 $63.84   9.516%   $69.915   $69.92   $69.90   $69.90  
  Purchase #3 $132.73   9.839%   $145.7893   $145.79   $145.80   $145.80  
  Purchase #4 $217.48   8.829%   $236.6813   $236.68   $236.70   $236.70  
  Purchase #5 $83.34   3.162%   $85.9752   $85.98   $86.00   $86.00  
  Purchase #6 $228.73   5.610%   $241.5618   $241.56   $241.55   $241.60  
  Purchase #7 $121.72   4.862%   $127.638   $127.64   $127.65   $127.60  
  7 purchase totals = $951.69       $1,024.1727   $1,024.18   $1,024.20   $1,024.20