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 $205.90   9.390%   $225.234   $225.23   $225.25   $225.20  
  Purchase #2 $86.82   7.351%   $93.2021   $93.20   $93.20   $93.20  
  Purchase #3 $64.83   7.573%   $69.7396   $69.74   $69.75   $69.70  
  Purchase #4 $109.96   13.360%   $124.6507   $124.65   $124.65   $124.70  
  Purchase #5 $146.93   4.871%   $154.087   $154.09   $154.10   $154.10  
  Purchase #6 $31.85   13.502%   $36.1504   $36.15   $36.15   $36.20  
  Purchase #7 $47.95   8.515%   $52.0329   $52.03   $52.05   $52.00  
  7 purchase totals = $694.24       $755.0967   $755.09   $755.15   $755.10