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	$126.89	9.574%	$139.0384	$139.04	$139.05	$139.00
Purchase #2	$9.66	3.761%	$10.0233	$10.02	$10.00	$10.00
Purchase #3	$67.40	5.494%	$71.103	$71.10	$71.10	$71.10
Purchase #4	$80.89	13.240%	$91.5998	$91.60	$91.60	$91.60
Purchase #5	$219.47	4.409%	$229.1464	$229.15	$229.15	$229.10
Purchase #6	$70.41	9.821%	$77.325	$77.33	$77.35	$77.30
Purchase #7	$142.48	3.764%	$147.8429	$147.84	$147.85	$147.80
7 purchase totals =	$717.20		$766.0788	$766.08	$766.10	$765.90