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 $151.87   11.116%   $168.7519   $168.75   $168.75   $168.80  
  Purchase #2 $53.88   12.143%   $60.4226   $60.42   $60.40   $60.40  
  Purchase #3 $38.68   9.718%   $42.4389   $42.44   $42.45   $42.40  
  Purchase #4 $162.49   4.564%   $169.906   $169.91   $169.90   $169.90  
  Purchase #5 $157.65   13.376%   $178.7373   $178.74   $178.75   $178.70  
  Purchase #6 $56.99   9.263%   $62.269   $62.27   $62.25   $62.30  
  Purchase #7 $65.97   10.672%   $73.0103   $73.01   $73.00   $73.00  
  7 purchase totals = $687.53       $755.5360   $755.54   $755.50   $755.50