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 $208.72   11.553%   $232.8334   $232.83   $232.85   $232.80  
  Purchase #2 $13.29   10.159%   $14.6401   $14.64   $14.65   $14.60  
  Purchase #3 $119.99   3.246%   $123.8849   $123.88   $123.90   $123.90  
  Purchase #4 $121.36   5.559%   $128.1064   $128.11   $128.10   $128.10  
  Purchase #5 $197.50   10.276%   $217.7951   $217.80   $217.80   $217.80  
  Purchase #6 $119.65   4.641%   $125.203   $125.20   $125.20   $125.20  
  Purchase #7 $71.72   11.531%   $79.99   $79.99   $80.00   $80.00  
  7 purchase totals = $852.23       $922.4529   $922.45   $922.50   $922.40