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	$83.92	11.719%	$93.7546	$93.75	$93.75	$93.80
Purchase #2	$205.55	11.217%	$228.6065	$228.61	$228.60	$228.60
Purchase #3	$39.62	9.557%	$43.4065	$43.41	$43.40	$43.40
Purchase #4	$67.74	6.169%	$71.9189	$71.92	$71.90	$71.90
Purchase #5	$191.55	12.801%	$216.0703	$216.07	$216.05	$216.10
Purchase #6	$31.88	3.248%	$32.9155	$32.92	$32.90	$32.90
Purchase #7	$71.31	12.417%	$80.1646	$80.16	$80.15	$80.20
7 purchase totals =	$691.57		$766.8369	$766.84	$766.75	$766.90