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	$18.57	5.815%	$19.6498	$19.65	$19.65	$19.60
Purchase #2	$24.71	4.820%	$25.901	$25.90	$25.90	$25.90
Purchase #3	$67.97	7.855%	$73.309	$73.31	$73.30	$73.30
Purchase #4	$162.34	6.512%	$172.9116	$172.91	$172.90	$172.90
Purchase #5	$36.86	7.782%	$39.7284	$39.73	$39.75	$39.70
Purchase #6	$247.27	11.526%	$275.7703	$275.77	$275.75	$275.80
Purchase #7	$39.69	9.590%	$43.4963	$43.50	$43.50	$43.50
7 purchase totals =	$597.41		$650.7664	$650.77	$650.75	$650.70