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	$79.92	4.489%	$83.5076	$83.51	$83.50	$83.50
Purchase #2	$140.48	10.697%	$155.5071	$155.51	$155.50	$155.50
Purchase #3	$215.39	10.656%	$238.342	$238.34	$238.35	$238.30
Purchase #4	$58.54	10.874%	$64.9056	$64.91	$64.90	$64.90
Purchase #5	$133.91	10.297%	$147.6987	$147.70	$147.70	$147.70
Purchase #6	$18.38	6.361%	$19.5492	$19.55	$19.55	$19.50
Purchase #7	$153.71	10.509%	$169.8634	$169.86	$169.85	$169.90
7 purchase totals =	$800.33		$879.3736	$879.38	$879.35	$879.30