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	$135.46	12.420%	$152.2841	$152.28	$152.30	$152.30
Purchase #2	$210.94	8.225%	$228.2898	$228.29	$228.30	$228.30
Purchase #3	$70.95	13.224%	$80.3324	$80.33	$80.35	$80.30
Purchase #4	$69.36	4.216%	$72.2842	$72.28	$72.30	$72.30
Purchase #5	$122.30	3.381%	$126.435	$126.44	$126.45	$126.40
Purchase #6	$129.25	10.248%	$142.4955	$142.50	$142.50	$142.50
Purchase #7	$109.28	12.814%	$123.2831	$123.28	$123.30	$123.30
7 purchase totals =	$847.54		$925.4041	$925.40	$925.50	$925.40