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 $236.27   6.363%   $251.3039   $251.30   $251.30   $251.30  
  Purchase #2 $62.28   6.747%   $66.482   $66.48   $66.50   $66.50  
  Purchase #3 $24.29   9.564%   $26.6131   $26.61   $26.60   $26.60  
  Purchase #4 $213.33   9.526%   $233.6518   $233.65   $233.65   $233.70  
  Purchase #5 $71.79   5.696%   $75.8792   $75.88   $75.90   $75.90  
  Purchase #6 $164.84   12.646%   $185.6857   $185.69   $185.70   $185.70  
  Purchase #7 $224.59   10.274%   $247.6644   $247.66   $247.65   $247.70  
  7 purchase totals = $997.39       $1,087.2801   $1,087.27   $1,087.30   $1,087.40