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	$198.48	4.544%	$207.4989	$207.50	$207.50	$207.50
Purchase #2	$118.87	3.496%	$123.0257	$123.03	$123.05	$123.00
Purchase #3	$250.86	4.460%	$262.0484	$262.05	$262.05	$262.00
Purchase #4	$37.99	7.774%	$40.9433	$40.94	$40.95	$40.90
Purchase #5	$243.73	11.530%	$271.8321	$271.83	$271.85	$271.80
Purchase #6	$94.91	3.448%	$98.1825	$98.18	$98.20	$98.20
Purchase #7	$84.29	6.154%	$89.4772	$89.48	$89.50	$89.50
7 purchase totals =	$1,029.13		$1,093.0081	$1,093.01	$1,093.10	$1,092.90