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	$231.56	12.404%	$260.2827	$260.28	$260.30	$260.30
Purchase #2	$96.63	3.378%	$99.8942	$99.89	$99.90	$99.90
Purchase #3	$27.44	3.148%	$28.3038	$28.30	$28.30	$28.30
Purchase #4	$221.77	8.287%	$240.1481	$240.15	$240.15	$240.10
Purchase #5	$166.76	7.204%	$178.7734	$178.77	$178.75	$178.80
Purchase #6	$98.56	12.766%	$111.1422	$111.14	$111.15	$111.10
Purchase #7	$91.86	9.375%	$100.4719	$100.47	$100.45	$100.50
7 purchase totals =	$934.58		$1,019.0163	$1,019.00	$1,019.00	$1,019.00