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	$165.97	3.592%	$171.9316	$171.93	$171.95	$171.90
Purchase #2	$67.96	9.484%	$74.4053	$74.41	$74.40	$74.40
Purchase #3	$202.52	3.202%	$209.0047	$209.00	$209.00	$209.00
Purchase #4	$170.45	11.632%	$190.2767	$190.28	$190.30	$190.30
Purchase #5	$168.81	5.678%	$178.395	$178.40	$178.40	$178.40
Purchase #6	$211.31	9.521%	$231.4288	$231.43	$231.45	$231.40
Purchase #7	$179.70	9.130%	$196.1066	$196.11	$196.10	$196.10
7 purchase totals =	$1,166.72		$1,251.5487	$1,251.56	$1,251.60	$1,251.50