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	$21.40	12.794%	$24.1379	$24.14	$24.15	$24.10
Purchase #2	$74.44	12.614%	$83.8299	$83.83	$83.85	$83.80
Purchase #3	$89.89	12.662%	$101.2719	$101.27	$101.25	$101.30
Purchase #4	$98.34	11.305%	$109.4573	$109.46	$109.45	$109.50
Purchase #5	$73.40	5.355%	$77.3306	$77.33	$77.35	$77.30
Purchase #6	$140.63	12.636%	$158.4	$158.40	$158.40	$158.40
Purchase #7	$213.47	7.361%	$229.1835	$229.18	$229.20	$229.20
7 purchase totals =	$711.57		$783.6111	$783.61	$783.65	$783.60