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 $196.69   6.535%   $209.5437   $209.54   $209.55   $209.50  
  Purchase #2 $248.41   13.790%   $282.6657   $282.67   $282.65   $282.70  
  Purchase #3 $72.32   3.413%   $74.7883   $74.79   $74.80   $74.80  
  Purchase #4 $38.80   6.513%   $41.327   $41.33   $41.35   $41.30  
  Purchase #5 $224.40   12.256%   $251.9025   $251.90   $251.90   $251.90  
  Purchase #6 $247.50   5.741%   $261.709   $261.71   $261.70   $261.70  
  Purchase #7 $125.98   5.729%   $133.1974   $133.20   $133.20   $133.20  
  7 purchase totals = $1,154.10       $1,255.1336   $1,255.14   $1,255.15   $1,255.10