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	$189.34	11.588%	$211.2807	$211.28	$211.30	$211.30
Purchase #2	$179.78	3.419%	$185.9267	$185.93	$185.95	$185.90
Purchase #3	$170.55	7.221%	$182.8654	$182.87	$182.85	$182.90
Purchase #4	$85.74	4.776%	$89.8349	$89.83	$89.85	$89.80
Purchase #5	$50.57	6.375%	$53.7938	$53.79	$53.80	$53.80
Purchase #6	$49.34	13.272%	$55.8884	$55.89	$55.90	$55.90
Purchase #7	$215.78	9.178%	$235.5843	$235.58	$235.60	$235.60
7 purchase totals =	$941.10		$1,015.1742	$1,015.17	$1,015.25	$1,015.20