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 $92.71   12.522%   $104.3191   $104.32   $104.30   $104.30  
  Purchase #2 $119.43   11.165%   $132.7644   $132.76   $132.75   $132.80  
  Purchase #3 $102.40   11.166%   $113.834   $113.83   $113.85   $113.80  
  Purchase #4 $8.51   5.506%   $8.9786   $8.98   $9.00   $9.00  
  Purchase #5 $174.92   7.317%   $187.7189   $187.72   $187.70   $187.70  
  Purchase #6 $16.67   5.867%   $17.648   $17.65   $17.65   $17.60  
  Purchase #7 $162.42   7.531%   $174.6519   $174.65   $174.65   $174.70  
  7 purchase totals = $677.06       $739.9149   $739.91   $739.90   $739.90