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	$75.79	5.793%	$80.1805	$80.18	$80.20	$80.20
Purchase #2	$248.92	5.580%	$262.8097	$262.81	$262.80	$262.80
Purchase #3	$91.73	13.809%	$104.397	$104.40	$104.40	$104.40
Purchase #4	$170.72	8.863%	$185.8509	$185.85	$185.85	$185.90
Purchase #5	$153.35	10.115%	$168.8614	$168.86	$168.85	$168.90
Purchase #6	$156.96	7.152%	$168.1858	$168.19	$168.20	$168.20
Purchase #7	$69.44	9.612%	$76.1146	$76.11	$76.10	$76.10
7 purchase totals =	$966.91		$1,046.3999	$1,046.40	$1,046.40	$1,046.50