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	$22.63	6.572%	$24.1172	$24.12	$24.10	$24.10
Purchase #2	$89.52	4.459%	$93.5117	$93.51	$93.50	$93.50
Purchase #3	$203.27	9.719%	$223.0258	$223.03	$223.05	$223.00
Purchase #4	$42.62	12.790%	$48.0711	$48.07	$48.05	$48.10
Purchase #5	$26.38	5.541%	$27.8417	$27.84	$27.85	$27.80
Purchase #6	$63.33	12.647%	$71.3393	$71.34	$71.35	$71.30
Purchase #7	$98.47	13.527%	$111.79	$111.79	$111.80	$111.80
7 purchase totals =	$546.22		$599.6968	$599.70	$599.70	$599.60