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 $65.87   7.527%   $70.828   $70.83   $70.85   $70.80  
  Purchase #2 $171.96   5.828%   $181.9818   $181.98   $182.00   $182.00  
  Purchase #3 $13.83   12.716%   $15.5886   $15.59   $15.60   $15.60  
  Purchase #4 $98.83   11.784%   $110.4761   $110.48   $110.50   $110.50  
  Purchase #5 $22.96   10.697%   $25.416   $25.42   $25.40   $25.40  
  Purchase #6 $106.40   11.686%   $118.8339   $118.83   $118.85   $118.80  
  Purchase #7 $199.33   4.757%   $208.8121   $208.81   $208.80   $208.80  
  7 purchase totals = $679.18       $731.9365   $731.94   $732.00   $731.90