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	$211.85	3.559%	$219.3897	$219.39	$219.40	$219.40
Purchase #2	$50.78	6.114%	$53.8847	$53.88	$53.90	$53.90
Purchase #3	$149.38	7.192%	$160.1234	$160.12	$160.10	$160.10
Purchase #4	$109.78	10.741%	$121.5715	$121.57	$121.55	$121.60
Purchase #5	$142.95	6.467%	$152.1946	$152.19	$152.20	$152.20
Purchase #6	$47.66	13.515%	$54.1012	$54.10	$54.10	$54.10
Purchase #7	$86.78	3.612%	$89.9145	$89.91	$89.90	$89.90
7 purchase totals =	$799.18		$851.1796	$851.16	$851.15	$851.20