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 $192.95   3.789%   $200.2609   $200.26   $200.25   $200.30  
  Purchase #2 $239.59   7.801%   $258.2804   $258.28   $258.30   $258.30  
  Purchase #3 $59.73   6.809%   $63.797   $63.80   $63.80   $63.80  
  Purchase #4 $67.38   11.710%   $75.2702   $75.27   $75.25   $75.30  
  Purchase #5 $26.70   12.234%   $29.9665   $29.97   $29.95   $30.00  
  Purchase #6 $209.94   10.446%   $231.8703   $231.87   $231.85   $231.90  
  Purchase #7 $6.95   7.872%   $7.4971   $7.50   $7.50   $7.50  
  7 purchase totals = $803.24       $866.9424   $866.95   $866.90   $867.10