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	$169.73	10.358%	$187.3106	$187.31	$187.30	$187.30
Purchase #2	$136.75	11.635%	$152.6609	$152.66	$152.65	$152.70
Purchase #3	$201.67	10.826%	$223.5028	$223.50	$223.50	$223.50
Purchase #4	$78.70	12.721%	$88.7114	$88.71	$88.70	$88.70
Purchase #5	$152.67	3.738%	$158.3768	$158.38	$158.40	$158.40
Purchase #6	$153.92	11.438%	$171.5254	$171.53	$171.55	$171.50
Purchase #7	$102.85	5.815%	$108.8307	$108.83	$108.85	$108.80
7 purchase totals =	$996.29		$1,090.9186	$1,090.92	$1,090.95	$1,090.90