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	$74.42	6.359%	$79.1524	$79.15	$79.15	$79.20
Purchase #2	$36.30	5.391%	$38.2569	$38.26	$38.25	$38.30
Purchase #3	$49.80	11.666%	$55.6097	$55.61	$55.60	$55.60
Purchase #4	$153.76	10.503%	$169.9094	$169.91	$169.90	$169.90
Purchase #5	$172.52	13.831%	$196.3812	$196.38	$196.40	$196.40
Purchase #6	$238.48	13.277%	$270.143	$270.14	$270.15	$270.10
Purchase #7	$161.90	8.437%	$175.5595	$175.56	$175.55	$175.60
7 purchase totals =	$887.18		$985.0121	$985.01	$985.00	$985.10