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	$81.93	10.103%	$90.2074	$90.21	$90.20	$90.20
Purchase #2	$240.73	9.857%	$264.4588	$264.46	$264.45	$264.50
Purchase #3	$238.81	13.204%	$270.3425	$270.34	$270.35	$270.30
Purchase #4	$169.72	9.781%	$186.3203	$186.32	$186.30	$186.30
Purchase #5	$82.48	3.704%	$85.5351	$85.54	$85.55	$85.50
Purchase #6	$199.83	11.177%	$222.165	$222.17	$222.15	$222.20
Purchase #7	$123.32	8.711%	$134.0624	$134.06	$134.05	$134.10
7 purchase totals =	$1,136.82		$1,253.0915	$1,253.10	$1,253.05	$1,253.10