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	$33.56	6.596%	$35.7736	$35.77	$35.75	$35.80
Purchase #2	$169.31	11.207%	$188.2846	$188.28	$188.30	$188.30
Purchase #3	$72.95	9.294%	$79.73	$79.73	$79.75	$79.70
Purchase #4	$70.80	13.809%	$80.5768	$80.58	$80.60	$80.60
Purchase #5	$64.61	4.220%	$67.3365	$67.34	$67.35	$67.30
Purchase #6	$99.80	4.430%	$104.2211	$104.22	$104.20	$104.20
Purchase #7	$29.25	12.518%	$32.9115	$32.91	$32.90	$32.90
7 purchase totals =	$540.28		$588.8341	$588.83	$588.85	$588.80