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	$85.95	4.607%	$89.9097	$89.91	$89.90	$89.90
Purchase #2	$103.33	8.453%	$112.0645	$112.06	$112.05	$112.10
Purchase #3	$244.60	9.248%	$267.2206	$267.22	$267.20	$267.20
Purchase #4	$55.53	6.206%	$58.9762	$58.98	$59.00	$59.00
Purchase #5	$212.74	10.827%	$235.7734	$235.77	$235.75	$235.80
Purchase #6	$231.94	9.416%	$253.7795	$253.78	$253.80	$253.80
Purchase #7	$155.96	9.754%	$171.1723	$171.17	$171.15	$171.20
7 purchase totals =	$1,090.05		$1,188.8962	$1,188.89	$1,188.85	$1,189.00