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	$34.48	9.629%	$37.8001	$37.80	$37.80	$37.80
Purchase #2	$174.82	6.268%	$185.7777	$185.78	$185.80	$185.80
Purchase #3	$186.79	6.139%	$198.257	$198.26	$198.25	$198.30
Purchase #4	$20.31	4.371%	$21.1978	$21.20	$21.20	$21.20
Purchase #5	$162.67	6.525%	$173.2842	$173.28	$173.30	$173.30
Purchase #6	$71.73	9.316%	$78.4124	$78.41	$78.40	$78.40
Purchase #7	$209.71	9.411%	$229.4458	$229.45	$229.45	$229.40
7 purchase totals =	$860.51		$924.1750	$924.18	$924.20	$924.20