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	$174.36	8.560%	$189.2852	$189.29	$189.30	$189.30
Purchase #2	$249.58	7.190%	$267.5248	$267.52	$267.50	$267.50
Purchase #3	$154.45	4.137%	$160.8396	$160.84	$160.85	$160.80
Purchase #4	$200.50	4.261%	$209.0433	$209.04	$209.05	$209.00
Purchase #5	$82.48	9.792%	$90.5564	$90.56	$90.55	$90.60
Purchase #6	$174.36	12.530%	$196.2073	$196.21	$196.20	$196.20
Purchase #7	$235.58	6.620%	$251.1754	$251.18	$251.20	$251.20
7 purchase totals =	$1,271.31		$1,364.6320	$1,364.64	$1,364.65	$1,364.60