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 $23.92   12.523%   $26.9155   $26.92   $26.90   $26.90  
  Purchase #2 $155.29   3.112%   $160.1226   $160.12   $160.10   $160.10  
  Purchase #3 $223.60   5.498%   $235.8935   $235.89   $235.90   $235.90  
  Purchase #4 $217.28   12.831%   $245.1592   $245.16   $245.15   $245.20  
  Purchase #5 $95.34   9.844%   $104.7253   $104.73   $104.75   $104.70  
  Purchase #6 $205.90   8.505%   $223.4118   $223.41   $223.40   $223.40  
  Purchase #7 $200.76   7.231%   $215.277   $215.28   $215.30   $215.30  
  7 purchase totals = $1,122.09       $1,211.5049   $1,211.51   $1,211.50   $1,211.50