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	$250.83	9.700%	$275.1605	$275.16	$275.15	$275.20
Purchase #2	$33.70	12.561%	$37.9331	$37.93	$37.95	$37.90
Purchase #3	$64.90	10.677%	$71.8294	$71.83	$71.85	$71.80
Purchase #4	$53.53	12.540%	$60.2427	$60.24	$60.25	$60.20
Purchase #5	$232.44	7.358%	$249.5429	$249.54	$249.55	$249.50
Purchase #6	$102.94	12.526%	$115.8343	$115.83	$115.85	$115.80
Purchase #7	$228.71	3.314%	$236.2894	$236.29	$236.30	$236.30
7 purchase totals =	$967.05		$1,046.8323	$1,046.82	$1,046.90	$1,046.70