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 $223.45   8.828%   $243.1762   $243.18   $243.20   $243.20  
  Purchase #2 $151.97   4.673%   $159.0716   $159.07   $159.05   $159.10  
  Purchase #3 $231.28   6.302%   $245.8553   $245.86   $245.85   $245.90  
  Purchase #4 $214.62   6.824%   $229.2657   $229.27   $229.25   $229.30  
  Purchase #5 $184.72   5.205%   $194.3347   $194.33   $194.35   $194.30  
  Purchase #6 $67.50   7.645%   $72.6604   $72.66   $72.65   $72.70  
  Purchase #7 $239.81   13.355%   $271.8366   $271.84   $271.85   $271.80  
  7 purchase totals = $1,313.35       $1,416.2005   $1,416.21   $1,416.20   $1,416.30