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	$40.67	12.718%	$45.8424	$45.84	$45.85	$45.80
Purchase #2	$137.63	10.794%	$152.4858	$152.49	$152.50	$152.50
Purchase #3	$155.98	7.801%	$168.148	$168.15	$168.15	$168.10
Purchase #4	$60.51	9.467%	$66.2385	$66.24	$66.25	$66.20
Purchase #5	$145.47	11.851%	$162.7096	$162.71	$162.70	$162.70
Purchase #6	$85.74	4.811%	$89.865	$89.87	$89.85	$89.90
Purchase #7	$115.96	12.521%	$130.4794	$130.48	$130.50	$130.50
7 purchase totals =	$741.96		$815.7687	$815.78	$815.80	$815.70