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	$248.34	9.343%	$271.5424	$271.54	$271.55	$271.50
Purchase #2	$120.45	5.819%	$127.459	$127.46	$127.45	$127.50
Purchase #3	$100.30	9.529%	$109.8576	$109.86	$109.85	$109.90
Purchase #4	$53.34	3.771%	$55.3515	$55.35	$55.35	$55.40
Purchase #5	$22.79	8.809%	$24.7976	$24.80	$24.80	$24.80
Purchase #6	$37.48	10.792%	$41.5248	$41.52	$41.50	$41.50
Purchase #7	$157.59	12.865%	$177.864	$177.86	$177.85	$177.90
7 purchase totals =	$740.29		$808.3969	$808.39	$808.35	$808.50