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	$78.71	13.598%	$89.413	$89.41	$89.40	$89.40
Purchase #2	$82.25	3.849%	$85.4158	$85.42	$85.40	$85.40
Purchase #3	$227.86	10.315%	$251.3638	$251.36	$251.35	$251.40
Purchase #4	$61.52	6.829%	$65.7212	$65.72	$65.70	$65.70
Purchase #5	$67.67	6.347%	$71.965	$71.97	$71.95	$72.00
Purchase #6	$223.96	5.115%	$235.4156	$235.42	$235.40	$235.40
Purchase #7	$165.63	11.654%	$184.9325	$184.93	$184.95	$184.90
7 purchase totals =	$907.60		$984.2269	$984.23	$984.15	$984.20