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	$40.33	13.834%	$45.9093	$45.91	$45.90	$45.90
Purchase #2	$242.82	13.310%	$275.1393	$275.14	$275.15	$275.10
Purchase #3	$111.98	7.147%	$119.9832	$119.98	$120.00	$120.00
Purchase #4	$216.36	11.842%	$241.9814	$241.98	$242.00	$242.00
Purchase #5	$202.25	3.560%	$209.4501	$209.45	$209.45	$209.50
Purchase #6	$33.43	4.762%	$35.0219	$35.02	$35.00	$35.00
Purchase #7	$188.79	3.567%	$195.5241	$195.52	$195.50	$195.50
7 purchase totals =	$1,035.96		$1,123.0093	$1,123.00	$1,123.00	$1,123.00