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	$67.78	7.775%	$73.0499	$73.05	$73.05	$73.00
Purchase #2	$42.98	6.448%	$45.7514	$45.75	$45.75	$45.80
Purchase #3	$118.81	12.828%	$134.0509	$134.05	$134.05	$134.10
Purchase #4	$16.90	8.133%	$18.2745	$18.27	$18.25	$18.30
Purchase #5	$81.40	10.142%	$89.6556	$89.66	$89.65	$89.70
Purchase #6	$223.31	9.673%	$244.9108	$244.91	$244.90	$244.90
Purchase #7	$246.88	7.313%	$264.9343	$264.93	$264.95	$264.90
7 purchase totals =	$798.06		$870.6274	$870.62	$870.60	$870.70