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	$87.64	8.749%	$95.3076	$95.31	$95.30	$95.30
Purchase #2	$74.41	6.133%	$78.9736	$78.97	$78.95	$79.00
Purchase #3	$219.90	7.467%	$236.3199	$236.32	$236.30	$236.30
Purchase #4	$72.81	7.477%	$78.254	$78.25	$78.25	$78.30
Purchase #5	$39.29	7.328%	$42.1692	$42.17	$42.15	$42.20
Purchase #6	$99.32	8.512%	$107.7741	$107.77	$107.75	$107.80
Purchase #7	$31.58	4.110%	$32.8779	$32.88	$32.90	$32.90
7 purchase totals =	$624.95		$671.6763	$671.67	$671.60	$671.80