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 $89.63   8.115%   $96.9035   $96.90   $96.90   $96.90  
  Purchase #2 $216.76   13.638%   $246.3217   $246.32   $246.30   $246.30  
  Purchase #3 $233.76   9.166%   $255.1864   $255.19   $255.20   $255.20  
  Purchase #4 $216.80   5.140%   $227.9435   $227.94   $227.95   $227.90  
  Purchase #5 $92.38   7.371%   $99.1893   $99.19   $99.20   $99.20  
  Purchase #6 $55.62   5.401%   $58.624   $58.62   $58.60   $58.60  
  Purchase #7 $35.82   3.163%   $36.953   $36.95   $36.95   $37.00  
  7 purchase totals = $940.77       $1,021.1214   $1,021.11   $1,021.10   $1,021.10