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	$37.46	3.468%	$38.7591	$38.76	$38.75	$38.80
Purchase #2	$80.84	10.531%	$89.3533	$89.35	$89.35	$89.40
Purchase #3	$178.70	11.276%	$198.8502	$198.85	$198.85	$198.90
Purchase #4	$92.97	10.624%	$102.8471	$102.85	$102.85	$102.80
Purchase #5	$142.48	4.153%	$148.3972	$148.40	$148.40	$148.40
Purchase #6	$137.36	13.530%	$155.9448	$155.94	$155.95	$155.90
Purchase #7	$220.32	10.325%	$243.068	$243.07	$243.05	$243.10
7 purchase totals =	$890.13		$977.2197	$977.22	$977.20	$977.30