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	$40.97	3.107%	$42.2429	$42.24	$42.25	$42.20
Purchase #2	$70.96	10.525%	$78.4285	$78.43	$78.45	$78.40
Purchase #3	$30.70	5.335%	$32.3378	$32.34	$32.35	$32.30
Purchase #4	$37.71	10.206%	$41.5587	$41.56	$41.55	$41.60
Purchase #5	$100.86	7.761%	$108.6877	$108.69	$108.70	$108.70
Purchase #6	$38.50	3.155%	$39.7147	$39.71	$39.70	$39.70
Purchase #7	$245.26	11.377%	$273.1632	$273.16	$273.15	$273.20
7 purchase totals =	$564.96		$616.1335	$616.13	$616.15	$616.10