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	$56.76	3.658%	$58.8363	$58.84	$58.85	$58.80
Purchase #2	$150.64	13.524%	$171.0126	$171.01	$171.00	$171.00
Purchase #3	$73.57	12.460%	$82.7368	$82.74	$82.75	$82.70
Purchase #4	$78.35	13.587%	$88.9954	$89.00	$89.00	$89.00
Purchase #5	$208.26	12.146%	$233.5553	$233.56	$233.55	$233.60
Purchase #6	$158.88	11.663%	$177.4102	$177.41	$177.40	$177.40
Purchase #7	$74.87	10.592%	$82.8002	$82.80	$82.80	$82.80
7 purchase totals =	$801.33		$895.3468	$895.36	$895.35	$895.30