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 $219.35   8.503%   $238.0013   $238.00   $238.00   $238.00  
  Purchase #2 $22.78   9.605%   $24.968   $24.97   $24.95   $25.00  
  Purchase #3 $77.40   6.617%   $82.5216   $82.52   $82.50   $82.50  
  Purchase #4 $54.77   13.173%   $61.9849   $61.98   $62.00   $62.00  
  Purchase #5 $195.91   6.304%   $208.2602   $208.26   $208.25   $208.30  
  Purchase #6 $107.68   8.647%   $116.9911   $116.99   $117.00   $117.00  
  Purchase #7 $36.59   7.180%   $39.2172   $39.22   $39.20   $39.20  
  7 purchase totals = $714.48       $771.9443   $771.94   $771.90   $772.00