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	$223.74	12.156%	$250.9378	$250.94	$250.95	$250.90
Purchase #2	$165.35	12.280%	$185.655	$185.66	$185.65	$185.70
Purchase #3	$188.71	5.401%	$198.9022	$198.90	$198.90	$198.90
Purchase #4	$186.72	12.513%	$210.0843	$210.08	$210.10	$210.10
Purchase #5	$235.36	13.655%	$267.4984	$267.50	$267.50	$267.50
Purchase #6	$208.87	7.161%	$223.8272	$223.83	$223.85	$223.80
Purchase #7	$247.71	12.221%	$277.9826	$277.98	$278.00	$278.00
7 purchase totals =	$1,456.46		$1,614.8875	$1,614.89	$1,614.95	$1,614.90