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	$73.65	4.568%	$77.0143	$77.01	$77.00	$77.00
Purchase #2	$93.90	4.662%	$98.2776	$98.28	$98.30	$98.30
Purchase #3	$191.90	10.758%	$212.5446	$212.54	$212.55	$212.50
Purchase #4	$42.53	6.322%	$45.2187	$45.22	$45.20	$45.20
Purchase #5	$6.74	6.679%	$7.1902	$7.19	$7.20	$7.20
Purchase #6	$53.77	10.203%	$59.2562	$59.26	$59.25	$59.30
Purchase #7	$101.86	9.610%	$111.6487	$111.65	$111.65	$111.60
7 purchase totals =	$564.35		$611.1503	$611.15	$611.15	$611.10