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 $141.95   6.734%   $151.5089   $151.51   $151.50   $151.50  
  Purchase #2 $225.66   12.429%   $253.7073   $253.71   $253.70   $253.70  
  Purchase #3 $153.83   10.414%   $169.8499   $169.85   $169.85   $169.80  
  Purchase #4 $127.71   13.352%   $144.7618   $144.76   $144.75   $144.80  
  Purchase #5 $177.84   8.113%   $192.2682   $192.27   $192.25   $192.30  
  Purchase #6 $214.36   9.181%   $234.0404   $234.04   $234.05   $234.00  
  Purchase #7 $137.38   13.385%   $155.7683   $155.77   $155.75   $155.80  
  7 purchase totals = $1,178.73       $1,301.9048   $1,301.91   $1,301.85   $1,301.90