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	$99.74	8.747%	$108.4643	$108.46	$108.45	$108.50
Purchase #2	$36.78	7.557%	$39.5595	$39.56	$39.55	$39.60
Purchase #3	$92.84	4.313%	$96.8442	$96.84	$96.85	$96.80
Purchase #4	$100.94	4.438%	$105.4197	$105.42	$105.40	$105.40
Purchase #5	$31.77	6.411%	$33.8068	$33.81	$33.80	$33.80
Purchase #6	$245.94	7.552%	$264.5134	$264.51	$264.50	$264.50
Purchase #7	$85.32	6.869%	$91.1806	$91.18	$91.20	$91.20
7 purchase totals =	$693.33		$739.7885	$739.78	$739.75	$739.80