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	$165.92	10.435%	$183.2338	$183.23	$183.25	$183.20
Purchase #2	$156.25	7.367%	$167.7609	$167.76	$167.75	$167.80
Purchase #3	$155.55	5.846%	$164.6435	$164.64	$164.65	$164.60
Purchase #4	$28.56	12.444%	$32.114	$32.11	$32.10	$32.10
Purchase #5	$85.75	9.425%	$93.8319	$93.83	$93.85	$93.80
Purchase #6	$112.43	7.279%	$120.6138	$120.61	$120.60	$120.60
Purchase #7	$150.81	3.840%	$156.6011	$156.60	$156.60	$156.60
7 purchase totals =	$855.27		$918.7990	$918.78	$918.80	$918.70