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	$31.47	9.611%	$34.4946	$34.49	$34.50	$34.50
Purchase #2	$159.71	7.518%	$171.717	$171.72	$171.70	$171.70
Purchase #3	$133.92	10.285%	$147.6937	$147.69	$147.70	$147.70
Purchase #4	$75.33	9.637%	$82.5896	$82.59	$82.60	$82.60
Purchase #5	$36.56	9.744%	$40.1224	$40.12	$40.10	$40.10
Purchase #6	$70.78	11.398%	$78.8475	$78.85	$78.85	$78.80
Purchase #7	$163.78	5.544%	$172.86	$172.86	$172.85	$172.90
7 purchase totals =	$671.55		$728.3248	$728.32	$728.30	$728.30