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	$80.41	6.317%	$85.4895	$85.49	$85.50	$85.50
Purchase #2	$47.56	11.582%	$53.0684	$53.07	$53.05	$53.10
Purchase #3	$43.99	12.652%	$49.5556	$49.56	$49.55	$49.60
Purchase #4	$177.94	4.114%	$185.2605	$185.26	$185.25	$185.30
Purchase #5	$235.44	12.362%	$264.5451	$264.55	$264.55	$264.50
Purchase #6	$19.43	9.553%	$21.2861	$21.29	$21.30	$21.30
Purchase #7	$59.54	7.658%	$64.0996	$64.10	$64.10	$64.10
7 purchase totals =	$664.31		$723.3048	$723.32	$723.30	$723.40