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	$75.68	3.315%	$78.1888	$78.19	$78.20	$78.20
Purchase #2	$228.25	6.237%	$242.486	$242.49	$242.50	$242.50
Purchase #3	$72.48	8.827%	$78.8778	$78.88	$78.90	$78.90
Purchase #4	$195.87	7.161%	$209.8963	$209.90	$209.90	$209.90
Purchase #5	$57.96	3.341%	$59.8964	$59.90	$59.90	$59.90
Purchase #6	$213.97	11.796%	$239.2099	$239.21	$239.20	$239.20
Purchase #7	$227.56	12.572%	$256.1688	$256.17	$256.15	$256.20
7 purchase totals =	$1,071.77		$1,164.7240	$1,164.74	$1,164.75	$1,164.80