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	$180.41	4.364%	$188.2831	$188.28	$188.30	$188.30
Purchase #2	$238.36	12.377%	$267.8618	$267.86	$267.85	$267.90
Purchase #3	$157.81	11.277%	$175.6062	$175.61	$175.60	$175.60
Purchase #4	$167.71	12.662%	$188.9454	$188.95	$188.95	$188.90
Purchase #5	$232.96	5.266%	$245.2277	$245.23	$245.25	$245.20
Purchase #6	$114.57	11.411%	$127.6436	$127.64	$127.65	$127.60
Purchase #7	$87.81	4.162%	$91.4647	$91.46	$91.45	$91.50
7 purchase totals =	$1,179.63		$1,285.0325	$1,285.03	$1,285.05	$1,285.00