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	$100.56	8.250%	$108.8562	$108.86	$108.85	$108.90
Purchase #2	$169.52	9.668%	$185.9092	$185.91	$185.90	$185.90
Purchase #3	$188.43	10.413%	$208.0512	$208.05	$208.05	$208.10
Purchase #4	$131.35	7.624%	$141.3641	$141.36	$141.35	$141.40
Purchase #5	$205.76	6.871%	$219.8978	$219.90	$219.90	$219.90
Purchase #6	$110.51	9.324%	$120.814	$120.81	$120.80	$120.80
Purchase #7	$129.62	13.197%	$146.726	$146.73	$146.75	$146.70
7 purchase totals =	$1,035.75		$1,131.6185	$1,131.62	$1,131.60	$1,131.70