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 $68.71   5.702%   $72.6278   $72.63   $72.65   $72.60  
  Purchase #2 $233.28   10.818%   $258.5162   $258.52   $258.50   $258.50  
  Purchase #3 $165.38   6.466%   $176.0735   $176.07   $176.05   $176.10  
  Purchase #4 $23.39   4.318%   $24.4   $24.40   $24.40   $24.40  
  Purchase #5 $233.77   4.581%   $244.479   $244.48   $244.50   $244.50  
  Purchase #6 $85.47   10.457%   $94.4076   $94.41   $94.40   $94.40  
  Purchase #7 $36.98   5.570%   $39.0398   $39.04   $39.05   $39.00  
  7 purchase totals = $846.98       $909.5439   $909.55   $909.55   $909.50