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	$148.25	13.483%	$168.2385	$168.24	$168.25	$168.20
Purchase #2	$129.67	5.179%	$136.3856	$136.39	$136.40	$136.40
Purchase #3	$81.97	9.414%	$89.6867	$89.69	$89.70	$89.70
Purchase #4	$105.46	4.711%	$110.4282	$110.43	$110.45	$110.40
Purchase #5	$45.39	7.142%	$48.6318	$48.63	$48.65	$48.60
Purchase #6	$59.51	13.201%	$67.3659	$67.37	$67.35	$67.40
Purchase #7	$64.58	12.619%	$72.7294	$72.73	$72.75	$72.70
7 purchase totals =	$634.83		$693.4661	$693.48	$693.55	$693.40