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	$33.72	12.363%	$37.8888	$37.89	$37.90	$37.90
Purchase #2	$121.31	13.326%	$137.4758	$137.48	$137.50	$137.50
Purchase #3	$18.46	13.470%	$20.9466	$20.95	$20.95	$20.90
Purchase #4	$248.28	10.586%	$274.5629	$274.56	$274.55	$274.60
Purchase #5	$15.50	4.722%	$16.2319	$16.23	$16.25	$16.20
Purchase #6	$223.92	5.743%	$236.7797	$236.78	$236.80	$236.80
Purchase #7	$110.36	13.191%	$124.9176	$124.92	$124.90	$124.90
7 purchase totals =	$771.55		$848.8033	$848.81	$848.85	$848.80