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 $218.55   8.229%   $236.5345   $236.53   $236.55   $236.50  
  Purchase #2 $206.77   13.801%   $235.3063   $235.31   $235.30   $235.30  
  Purchase #3 $205.85   13.742%   $234.1379   $234.14   $234.15   $234.10  
  Purchase #4 $211.91   4.601%   $221.66   $221.66   $221.65   $221.70  
  Purchase #5 $92.47   6.377%   $98.3668   $98.37   $98.35   $98.40  
  Purchase #6 $219.48   12.635%   $247.2113   $247.21   $247.20   $247.20  
  Purchase #7 $108.96   10.414%   $120.3071   $120.31   $120.30   $120.30  
  7 purchase totals = $1,263.99       $1,393.5239   $1,393.53   $1,393.50   $1,393.50