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	$10.61	11.335%	$11.8126	$11.81	$11.80	$11.80
Purchase #2	$238.74	4.866%	$250.3571	$250.36	$250.35	$250.40
Purchase #3	$36.45	13.735%	$41.4564	$41.46	$41.45	$41.50
Purchase #4	$55.69	10.442%	$61.5051	$61.51	$61.50	$61.50
Purchase #5	$110.68	7.629%	$119.1238	$119.12	$119.10	$119.10
Purchase #6	$217.39	9.814%	$238.7247	$238.72	$238.70	$238.70
Purchase #7	$190.46	11.561%	$212.4791	$212.48	$212.50	$212.50
7 purchase totals =	$860.02		$935.4588	$935.46	$935.40	$935.50