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	$65.43	8.231%	$70.8155	$70.82	$70.80	$70.80
Purchase #2	$85.71	6.236%	$91.0549	$91.05	$91.05	$91.10
Purchase #3	$55.31	6.424%	$58.8631	$58.86	$58.85	$58.90
Purchase #4	$42.69	7.251%	$45.7855	$45.79	$45.80	$45.80
Purchase #5	$127.43	11.816%	$142.4871	$142.49	$142.50	$142.50
Purchase #6	$25.44	6.772%	$27.1628	$27.16	$27.15	$27.20
Purchase #7	$51.48	6.572%	$54.8633	$54.86	$54.85	$54.90
7 purchase totals =	$453.49		$491.0322	$491.03	$491.00	$491.20