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	$168.34	12.476%	$189.3421	$189.34	$189.35	$189.30
Purchase #2	$80.41	5.372%	$84.7296	$84.73	$84.75	$84.70
Purchase #3	$77.29	4.217%	$80.5493	$80.55	$80.55	$80.50
Purchase #4	$223.41	3.627%	$231.5131	$231.51	$231.50	$231.50
Purchase #5	$200.52	11.665%	$223.9107	$223.91	$223.90	$223.90
Purchase #6	$8.49	10.501%	$9.3815	$9.38	$9.40	$9.40
Purchase #7	$164.83	11.815%	$184.3047	$184.30	$184.30	$184.30
7 purchase totals =	$923.29		$1,003.7310	$1,003.72	$1,003.75	$1,003.60