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 $81.54   13.474%   $92.5267   $92.53   $92.55   $92.50  
  Purchase #2 $95.37   11.752%   $106.5779   $106.58   $106.60   $106.60  
  Purchase #3 $9.88   6.496%   $10.5218   $10.52   $10.50   $10.50  
  Purchase #4 $63.29   4.271%   $65.9931   $65.99   $66.00   $66.00  
  Purchase #5 $56.61   9.355%   $61.9059   $61.91   $61.90   $61.90  
  Purchase #6 $238.56   8.553%   $258.964   $258.96   $258.95   $259.00  
  Purchase #7 $129.73   12.350%   $145.7517   $145.75   $145.75   $145.80  
  7 purchase totals = $674.98       $742.2411   $742.24   $742.25   $742.30