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 $217.54   7.849%   $234.6147   $234.61   $234.60   $234.60  
  Purchase #2 $209.87   6.651%   $223.8285   $223.83   $223.85   $223.80  
  Purchase #3 $131.35   8.619%   $142.6711   $142.67   $142.65   $142.70  
  Purchase #4 $11.81   10.519%   $13.0523   $13.05   $13.05   $13.10  
  Purchase #5 $187.60   7.300%   $201.2948   $201.29   $201.30   $201.30  
  Purchase #6 $126.50   6.362%   $134.5479   $134.55   $134.55   $134.50  
  Purchase #7 $17.26   3.302%   $17.8299   $17.83   $17.85   $17.80  
  7 purchase totals = $901.93       $967.8392   $967.83   $967.85   $967.80