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	$49.84	10.311%	$54.979	$54.98	$55.00	$55.00
Purchase #2	$57.73	6.238%	$61.3312	$61.33	$61.35	$61.30
Purchase #3	$131.38	6.391%	$139.7765	$139.78	$139.80	$139.80
Purchase #4	$245.89	9.605%	$269.5077	$269.51	$269.50	$269.50
Purchase #5	$68.61	3.601%	$71.0806	$71.08	$71.10	$71.10
Purchase #6	$64.96	8.639%	$70.5719	$70.57	$70.55	$70.60
Purchase #7	$198.33	11.373%	$220.8861	$220.89	$220.90	$220.90
7 purchase totals =	$816.74		$888.1330	$888.14	$888.20	$888.20