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	$103.31	12.194%	$115.9076	$115.91	$115.90	$115.90
Purchase #2	$73.73	12.244%	$82.7575	$82.76	$82.75	$82.80
Purchase #3	$195.36	13.843%	$222.4037	$222.40	$222.40	$222.40
Purchase #4	$66.84	8.822%	$72.7366	$72.74	$72.75	$72.70
Purchase #5	$8.59	3.449%	$8.8863	$8.89	$8.90	$8.90
Purchase #6	$139.72	5.578%	$147.5136	$147.51	$147.50	$147.50
Purchase #7	$107.41	10.358%	$118.5355	$118.54	$118.55	$118.50
7 purchase totals =	$694.96		$768.7408	$768.75	$768.75	$768.70