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	$134.34	9.363%	$146.9183	$146.92	$146.90	$146.90
Purchase #2	$100.62	4.610%	$105.2586	$105.26	$105.25	$105.30
Purchase #3	$31.60	12.350%	$35.5026	$35.50	$35.50	$35.50
Purchase #4	$21.40	11.856%	$23.9372	$23.94	$23.95	$23.90
Purchase #5	$138.53	11.377%	$154.2906	$154.29	$154.30	$154.30
Purchase #6	$142.62	3.760%	$147.9825	$147.98	$148.00	$148.00
Purchase #7	$212.96	4.410%	$222.3515	$222.35	$222.35	$222.40
7 purchase totals =	$782.07		$836.2413	$836.24	$836.25	$836.30