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	$37.40	3.804%	$38.8227	$38.82	$38.80	$38.80
Purchase #2	$36.61	12.272%	$41.1028	$41.10	$41.10	$41.10
Purchase #3	$247.67	12.367%	$278.2993	$278.30	$278.30	$278.30
Purchase #4	$199.69	9.260%	$218.1813	$218.18	$218.20	$218.20
Purchase #5	$240.54	4.600%	$251.6048	$251.60	$251.60	$251.60
Purchase #6	$248.89	10.737%	$275.6133	$275.61	$275.60	$275.60
Purchase #7	$76.30	12.560%	$85.8833	$85.88	$85.90	$85.90
7 purchase totals =	$1,087.10		$1,189.5075	$1,189.49	$1,189.50	$1,189.50