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	$67.50	5.418%	$71.1572	$71.16	$71.15	$71.20
Purchase #2	$22.77	9.517%	$24.937	$24.94	$24.95	$24.90
Purchase #3	$130.69	5.119%	$137.38	$137.38	$137.40	$137.40
Purchase #4	$67.67	9.248%	$73.9281	$73.93	$73.95	$73.90
Purchase #5	$23.99	5.375%	$25.2795	$25.28	$25.30	$25.30
Purchase #6	$83.52	8.632%	$90.7294	$90.73	$90.75	$90.70
Purchase #7	$89.33	11.732%	$99.8102	$99.81	$99.80	$99.80
7 purchase totals =	$485.47		$523.2214	$523.23	$523.30	$523.20