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 $230.53   10.793%   $255.4111   $255.41   $255.40   $255.40  
  Purchase #2 $164.82   10.203%   $181.6366   $181.64   $181.65   $181.60  
  Purchase #3 $197.47   12.268%   $221.6956   $221.70   $221.70   $221.70  
  Purchase #4 $120.97   9.537%   $132.5069   $132.51   $132.50   $132.50  
  Purchase #5 $46.80   6.584%   $49.8813   $49.88   $49.90   $49.90  
  Purchase #6 $13.47   13.758%   $15.3232   $15.32   $15.30   $15.30  
  Purchase #7 $84.48   13.868%   $96.1957   $96.20   $96.20   $96.20  
  7 purchase totals = $858.54       $952.6504   $952.66   $952.65   $952.60