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	$65.90	7.379%	$70.7628	$70.76	$70.75	$70.80
Purchase #2	$46.70	3.605%	$48.3835	$48.38	$48.40	$48.40
Purchase #3	$56.94	6.820%	$60.8233	$60.82	$60.80	$60.80
Purchase #4	$243.73	8.857%	$265.3172	$265.32	$265.30	$265.30
Purchase #5	$165.50	4.413%	$172.8035	$172.80	$172.80	$172.80
Purchase #6	$236.95	10.362%	$261.5028	$261.50	$261.50	$261.50
Purchase #7	$56.56	5.258%	$59.5339	$59.53	$59.55	$59.50
7 purchase totals =	$872.28		$939.1270	$939.11	$939.10	$939.10