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	$75.96	6.810%	$81.1329	$81.13	$81.15	$81.10
Purchase #2	$33.64	12.785%	$37.9409	$37.94	$37.95	$37.90
Purchase #3	$224.55	9.123%	$245.0357	$245.04	$245.05	$245.00
Purchase #4	$80.81	13.215%	$91.489	$91.49	$91.50	$91.50
Purchase #5	$229.48	11.800%	$256.5586	$256.56	$256.55	$256.60
Purchase #6	$48.33	4.298%	$50.4072	$50.41	$50.40	$50.40
Purchase #7	$79.91	3.367%	$82.6006	$82.60	$82.60	$82.60
7 purchase totals =	$772.68		$845.1649	$845.17	$845.20	$845.10