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	$110.84	9.471%	$121.3377	$121.34	$121.35	$121.30
Purchase #2	$67.70	7.751%	$72.9474	$72.95	$72.95	$72.90
Purchase #3	$136.90	13.557%	$155.4595	$155.46	$155.45	$155.50
Purchase #4	$157.47	5.598%	$166.2852	$166.29	$166.30	$166.30
Purchase #5	$51.90	6.637%	$55.3446	$55.34	$55.35	$55.30
Purchase #6	$28.90	11.146%	$32.1212	$32.12	$32.10	$32.10
Purchase #7	$244.64	10.578%	$270.518	$270.52	$270.50	$270.50
7 purchase totals =	$798.35		$874.0136	$874.02	$874.00	$873.90