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	$32.88	7.229%	$35.2569	$35.26	$35.25	$35.30
Purchase #2	$140.89	7.823%	$151.9118	$151.91	$151.90	$151.90
Purchase #3	$91.31	9.270%	$99.7744	$99.77	$99.75	$99.80
Purchase #4	$212.39	13.736%	$241.5639	$241.56	$241.55	$241.60
Purchase #5	$151.26	4.819%	$158.5492	$158.55	$158.55	$158.50
Purchase #6	$74.37	5.438%	$78.4142	$78.41	$78.40	$78.40
Purchase #7	$67.38	3.450%	$69.7046	$69.70	$69.70	$69.70
7 purchase totals =	$770.48		$835.1750	$835.16	$835.10	$835.20