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	$154.57	6.429%	$164.5073	$164.51	$164.50	$164.50
Purchase #2	$34.76	4.450%	$36.3068	$36.31	$36.30	$36.30
Purchase #3	$228.33	9.427%	$249.8547	$249.85	$249.85	$249.90
Purchase #4	$165.55	3.658%	$171.6058	$171.61	$171.60	$171.60
Purchase #5	$45.42	11.300%	$50.5525	$50.55	$50.55	$50.60
Purchase #6	$117.37	4.140%	$122.2291	$122.23	$122.25	$122.20
Purchase #7	$134.93	11.380%	$150.285	$150.29	$150.30	$150.30
7 purchase totals =	$880.93		$945.3412	$945.35	$945.35	$945.40