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	$93.81	6.444%	$99.8551	$99.86	$99.85	$99.90
Purchase #2	$45.51	9.676%	$49.9135	$49.91	$49.90	$49.90
Purchase #3	$210.72	5.490%	$222.2885	$222.29	$222.30	$222.30
Purchase #4	$52.36	9.674%	$57.4253	$57.43	$57.45	$57.40
Purchase #5	$59.97	12.712%	$67.5934	$67.59	$67.60	$67.60
Purchase #6	$167.96	6.249%	$178.4558	$178.46	$178.45	$178.50
Purchase #7	$71.50	9.422%	$78.2367	$78.24	$78.25	$78.20
7 purchase totals =	$701.83		$753.7683	$753.78	$753.80	$753.80