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 $153.69   9.153%   $167.7572   $167.76   $167.75   $167.80  
  Purchase #2 $5.63   12.415%   $6.329   $6.33   $6.35   $6.30  
  Purchase #3 $141.65   3.698%   $146.8882   $146.89   $146.90   $146.90  
  Purchase #4 $46.25   13.801%   $52.633   $52.63   $52.65   $52.60  
  Purchase #5 $172.48   13.115%   $195.1008   $195.10   $195.10   $195.10  
  Purchase #6 $127.32   7.487%   $136.8524   $136.85   $136.85   $136.90  
  Purchase #7 $24.58   10.503%   $27.1616   $27.16   $27.15   $27.20  
  7 purchase totals = $671.60       $732.7222   $732.72   $732.75   $732.80