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 $222.28   4.386%   $232.0292   $232.03   $232.05   $232.00  
  Purchase #2 $228.74   7.835%   $246.6618   $246.66   $246.65   $246.70  
  Purchase #3 $31.29   7.365%   $33.5945   $33.59   $33.60   $33.60  
  Purchase #4 $73.30   4.128%   $76.3258   $76.33   $76.35   $76.30  
  Purchase #5 $204.90   9.354%   $224.0663   $224.07   $224.05   $224.10  
  Purchase #6 $190.45   13.298%   $215.776   $215.78   $215.80   $215.80  
  Purchase #7 $204.83   5.160%   $215.3992   $215.40   $215.40   $215.40  
  7 purchase totals = $1,155.79       $1,243.8528   $1,243.86   $1,243.90   $1,243.90