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	$211.49	6.493%	$225.222	$225.22	$225.20	$225.20
Purchase #2	$160.27	6.628%	$170.8927	$170.89	$170.90	$170.90
Purchase #3	$38.38	11.144%	$42.6571	$42.66	$42.65	$42.70
Purchase #4	$89.26	10.864%	$98.9572	$98.96	$98.95	$99.00
Purchase #5	$32.86	9.280%	$35.9094	$35.91	$35.90	$35.90
Purchase #6	$88.90	8.786%	$96.7108	$96.71	$96.70	$96.70
Purchase #7	$21.36	6.732%	$22.798	$22.80	$22.80	$22.80
7 purchase totals =	$642.52		$693.1472	$693.15	$693.10	$693.20