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 $88.83   8.312%   $96.2135   $96.21   $96.20   $96.20  
  Purchase #2 $147.83   6.136%   $156.9008   $156.90   $156.90   $156.90  
  Purchase #3 $14.96   5.201%   $15.7381   $15.74   $15.75   $15.70  
  Purchase #4 $93.89   11.534%   $104.7193   $104.72   $104.70   $104.70  
  Purchase #5 $161.78   8.702%   $175.8581   $175.86   $175.85   $175.90  
  Purchase #6 $20.98   12.680%   $23.6403   $23.64   $23.65   $23.60  
  Purchase #7 $118.73   6.687%   $126.6695   $126.67   $126.65   $126.70  
  7 purchase totals = $647.00       $699.7396   $699.74   $699.70   $699.70