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	$105.93	13.766%	$120.5123	$120.51	$120.50	$120.50
Purchase #2	$44.96	7.386%	$48.2807	$48.28	$48.30	$48.30
Purchase #3	$94.99	6.459%	$101.1254	$101.13	$101.15	$101.10
Purchase #4	$219.28	13.299%	$248.442	$248.44	$248.45	$248.40
Purchase #5	$36.71	6.627%	$39.1428	$39.14	$39.15	$39.10
Purchase #6	$86.32	4.642%	$90.327	$90.33	$90.35	$90.30
Purchase #7	$84.82	5.568%	$89.5428	$89.54	$89.55	$89.50
7 purchase totals =	$673.01		$737.3730	$737.37	$737.45	$737.20