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	$77.36	7.661%	$83.2865	$83.29	$83.30	$83.30
Purchase #2	$168.37	6.761%	$179.7535	$179.75	$179.75	$179.80
Purchase #3	$25.91	11.314%	$28.8415	$28.84	$28.85	$28.80
Purchase #4	$69.47	5.552%	$73.327	$73.33	$73.35	$73.30
Purchase #5	$40.99	3.623%	$42.4751	$42.48	$42.50	$42.50
Purchase #6	$152.94	13.610%	$173.7551	$173.76	$173.75	$173.80
Purchase #7	$122.78	13.695%	$139.5947	$139.59	$139.60	$139.60
7 purchase totals =	$657.82		$721.0334	$721.04	$721.10	$721.10