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 $91.81   4.702%   $96.1269   $96.13   $96.15   $96.10  
  Purchase #2 $32.47   13.339%   $36.8012   $36.80   $36.80   $36.80  
  Purchase #3 $103.47   13.826%   $117.7758   $117.78   $117.80   $117.80  
  Purchase #4 $216.73   13.800%   $246.6387   $246.64   $246.65   $246.60  
  Purchase #5 $142.31   8.816%   $154.856   $154.86   $154.85   $154.90  
  Purchase #6 $94.68   4.298%   $98.7493   $98.75   $98.75   $98.70  
  Purchase #7 $61.83   13.192%   $69.9866   $69.99   $70.00   $70.00  
  7 purchase totals = $743.30       $820.9345   $820.95   $821.00   $820.90