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 $165.52   10.544%   $182.9724   $182.97   $182.95   $183.00  
  Purchase #2 $186.76   13.460%   $211.8979   $211.90   $211.90   $211.90  
  Purchase #3 $74.75   10.544%   $82.6316   $82.63   $82.65   $82.60  
  Purchase #4 $14.89   8.458%   $16.1494   $16.15   $16.15   $16.10  
  Purchase #5 $36.33   3.632%   $37.6495   $37.65   $37.65   $37.60  
  Purchase #6 $240.56   5.531%   $253.8654   $253.87   $253.85   $253.90  
  Purchase #7 $166.74   7.390%   $179.0621   $179.06   $179.05   $179.10  
  7 purchase totals = $885.55       $964.2283   $964.23   $964.20   $964.20