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	$183.42	3.249%	$189.3793	$189.38	$189.40	$189.40
Purchase #2	$82.90	8.171%	$89.6738	$89.67	$89.65	$89.70
Purchase #3	$229.38	5.556%	$242.1244	$242.12	$242.10	$242.10
Purchase #4	$94.31	12.569%	$106.1638	$106.16	$106.15	$106.20
Purchase #5	$83.34	13.614%	$94.6859	$94.69	$94.70	$94.70
Purchase #6	$88.90	11.320%	$98.9635	$98.96	$98.95	$99.00
Purchase #7	$156.82	11.733%	$175.2197	$175.22	$175.20	$175.20
7 purchase totals =	$919.07		$996.2104	$996.20	$996.15	$996.30