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 $44.93   8.585%   $48.7872   $48.79   $48.80   $48.80  
  Purchase #2 $174.95   13.535%   $198.6295   $198.63   $198.65   $198.60  
  Purchase #3 $34.43   9.502%   $37.7015   $37.70   $37.70   $37.70  
  Purchase #4 $27.91   6.777%   $29.8015   $29.80   $29.80   $29.80  
  Purchase #5 $80.63   11.394%   $89.817   $89.82   $89.80   $89.80  
  Purchase #6 $212.26   11.804%   $237.3152   $237.32   $237.30   $237.30  
  Purchase #7 $154.47   5.283%   $162.6307   $162.63   $162.65   $162.60  
  7 purchase totals = $729.58       $804.6826   $804.69   $804.70   $804.60