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	$24.95	12.489%	$28.066	$28.07	$28.05	$28.10
Purchase #2	$239.86	6.865%	$256.3264	$256.33	$256.35	$256.30
Purchase #3	$88.27	9.767%	$96.8913	$96.89	$96.90	$96.90
Purchase #4	$172.63	10.283%	$190.3815	$190.38	$190.40	$190.40
Purchase #5	$32.48	10.735%	$35.9667	$35.97	$35.95	$36.00
Purchase #6	$153.87	13.236%	$174.2362	$174.24	$174.25	$174.20
Purchase #7	$7.46	6.242%	$7.9257	$7.93	$7.95	$7.90
7 purchase totals =	$719.52		$789.7938	$789.81	$789.85	$789.80