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	$96.27	3.285%	$99.4325	$99.43	$99.45	$99.40
Purchase #2	$29.41	12.251%	$33.013	$33.01	$33.00	$33.00
Purchase #3	$247.76	12.360%	$278.3831	$278.38	$278.40	$278.40
Purchase #4	$36.25	3.576%	$37.5463	$37.55	$37.55	$37.50
Purchase #5	$80.39	12.586%	$90.5079	$90.51	$90.50	$90.50
Purchase #6	$108.85	7.721%	$117.2543	$117.25	$117.25	$117.30
Purchase #7	$6.64	7.485%	$7.137	$7.14	$7.15	$7.10
7 purchase totals =	$605.57		$663.2741	$663.27	$663.30	$663.20