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	$89.64	5.399%	$94.4797	$94.48	$94.50	$94.50
Purchase #2	$78.92	13.723%	$89.7502	$89.75	$89.75	$89.80
Purchase #3	$82.56	6.520%	$87.9429	$87.94	$87.95	$87.90
Purchase #4	$5.76	13.762%	$6.5527	$6.55	$6.55	$6.60
Purchase #5	$18.70	3.543%	$19.3625	$19.36	$19.35	$19.40
Purchase #6	$119.46	9.181%	$130.4276	$130.43	$130.45	$130.40
Purchase #7	$93.41	9.515%	$102.298	$102.30	$102.30	$102.30
7 purchase totals =	$488.45		$530.8136	$530.81	$530.85	$530.90