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 $88.48   10.279%   $97.5749   $97.57   $97.55   $97.60  
  Purchase #2 $14.73   6.540%   $15.6933   $15.69   $15.70   $15.70  
  Purchase #3 $108.91   11.697%   $121.6492   $121.65   $121.65   $121.60  
  Purchase #4 $216.51   11.236%   $240.8371   $240.84   $240.85   $240.80  
  Purchase #5 $133.76   6.655%   $142.6617   $142.66   $142.65   $142.70  
  Purchase #6 $113.80   10.647%   $125.9163   $125.92   $125.90   $125.90  
  Purchase #7 $10.76   12.214%   $12.0742   $12.07   $12.05   $12.10  
  7 purchase totals = $686.95       $756.4067   $756.40   $756.35   $756.40