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	$92.95	7.274%	$99.7112	$99.71	$99.70	$99.70
Purchase #2	$56.41	9.642%	$61.8491	$61.85	$61.85	$61.80
Purchase #3	$33.61	9.413%	$36.7737	$36.77	$36.75	$36.80
Purchase #4	$33.40	10.582%	$36.9344	$36.93	$36.95	$36.90
Purchase #5	$168.65	6.382%	$179.4132	$179.41	$179.40	$179.40
Purchase #6	$55.65	9.368%	$60.8633	$60.86	$60.85	$60.90
Purchase #7	$40.61	12.818%	$45.8154	$45.82	$45.80	$45.80
7 purchase totals =	$481.28		$521.3603	$521.35	$521.30	$521.30