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 $168.98   6.709%   $180.3169   $180.32   $180.30   $180.30  
  Purchase #2 $241.93   5.780%   $255.9136   $255.91   $255.90   $255.90  
  Purchase #3 $169.77   11.568%   $189.409   $189.41   $189.40   $189.40  
  Purchase #4 $154.74   13.801%   $176.0957   $176.10   $176.10   $176.10  
  Purchase #5 $206.38   13.615%   $234.4786   $234.48   $234.50   $234.50  
  Purchase #6 $95.53   9.560%   $104.6627   $104.66   $104.65   $104.70  
  Purchase #7 $238.65   6.294%   $253.6706   $253.67   $253.65   $253.70  
  7 purchase totals = $1,275.98       $1,394.5471   $1,394.55   $1,394.50   $1,394.60