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	$35.54	3.658%	$36.8401	$36.84	$36.85	$36.80
Purchase #2	$79.71	4.280%	$83.1216	$83.12	$83.10	$83.10
Purchase #3	$189.71	3.688%	$196.7065	$196.71	$196.70	$196.70
Purchase #4	$155.73	6.323%	$165.5768	$165.58	$165.60	$165.60
Purchase #5	$111.56	12.345%	$125.3321	$125.33	$125.35	$125.30
Purchase #6	$19.26	3.105%	$19.858	$19.86	$19.85	$19.90
Purchase #7	$118.38	10.281%	$130.5506	$130.55	$130.55	$130.60
7 purchase totals =	$709.89		$757.9857	$757.99	$758.00	$758.00