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	$42.72	7.420%	$45.8898	$45.89	$45.90	$45.90
Purchase #2	$130.29	11.633%	$145.4466	$145.45	$145.45	$145.40
Purchase #3	$171.84	3.275%	$177.4678	$177.47	$177.45	$177.50
Purchase #4	$24.46	10.576%	$27.0469	$27.05	$27.05	$27.00
Purchase #5	$33.66	11.842%	$37.646	$37.65	$37.65	$37.60
Purchase #6	$102.28	11.224%	$113.7599	$113.76	$113.75	$113.80
Purchase #7	$249.45	9.774%	$273.8312	$273.83	$273.85	$273.80
7 purchase totals =	$754.70		$821.0882	$821.10	$821.10	$821.00