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	$168.53	12.245%	$189.1665	$189.17	$189.15	$189.20
Purchase #2	$181.76	7.840%	$196.01	$196.01	$196.00	$196.00
Purchase #3	$110.75	13.261%	$125.4366	$125.44	$125.45	$125.40
Purchase #4	$52.56	5.746%	$55.5801	$55.58	$55.60	$55.60
Purchase #5	$84.69	4.447%	$88.4562	$88.46	$88.45	$88.50
Purchase #6	$247.63	4.805%	$259.5286	$259.53	$259.55	$259.50
Purchase #7	$221.47	13.257%	$250.8303	$250.83	$250.85	$250.80
7 purchase totals =	$1,067.39		$1,165.0083	$1,165.02	$1,165.05	$1,165.00