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 $208.92   8.774%   $227.2506   $227.25   $227.25   $227.30  
  Purchase #2 $69.76   3.574%   $72.2532   $72.25   $72.25   $72.30  
  Purchase #3 $141.41   3.805%   $146.7907   $146.79   $146.80   $146.80  
  Purchase #4 $190.65   6.772%   $203.5608   $203.56   $203.55   $203.60  
  Purchase #5 $91.56   10.471%   $101.1472   $101.15   $101.15   $101.10  
  Purchase #6 $6.46   11.408%   $7.197   $7.20   $7.20   $7.20  
  Purchase #7 $172.77   12.290%   $194.0034   $194.00   $194.00   $194.00  
  7 purchase totals = $881.53       $952.2029   $952.20   $952.20   $952.30