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	$76.99	8.514%	$83.5449	$83.54	$83.55	$83.50
Purchase #2	$123.86	13.774%	$140.9205	$140.92	$140.90	$140.90
Purchase #3	$6.35	7.359%	$6.8173	$6.82	$6.80	$6.80
Purchase #4	$8.54	11.512%	$9.5231	$9.52	$9.50	$9.50
Purchase #5	$115.75	13.829%	$131.7571	$131.76	$131.75	$131.80
Purchase #6	$139.30	8.694%	$151.4107	$151.41	$151.40	$151.40
Purchase #7	$10.81	3.352%	$11.1724	$11.17	$11.15	$11.20
7 purchase totals =	$481.60		$535.1460	$535.14	$535.05	$535.10