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	$240.73	4.192%	$250.8214	$250.82	$250.80	$250.80
Purchase #2	$93.37	13.479%	$105.9553	$105.96	$105.95	$106.00
Purchase #3	$90.76	11.129%	$100.8607	$100.86	$100.85	$100.90
Purchase #4	$84.67	7.832%	$91.3014	$91.30	$91.30	$91.30
Purchase #5	$209.70	7.360%	$225.1339	$225.13	$225.15	$225.10
Purchase #6	$84.57	7.294%	$90.7385	$90.74	$90.75	$90.70
Purchase #7	$33.82	7.774%	$36.4492	$36.45	$36.45	$36.40
7 purchase totals =	$837.62		$901.2604	$901.26	$901.25	$901.20