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	$33.92	5.504%	$35.787	$35.79	$35.80	$35.80
Purchase #2	$158.72	11.248%	$176.5728	$176.57	$176.55	$176.60
Purchase #3	$67.61	8.621%	$73.4387	$73.44	$73.45	$73.40
Purchase #4	$56.90	3.784%	$59.0531	$59.05	$59.05	$59.10
Purchase #5	$6.33	13.410%	$7.1789	$7.18	$7.20	$7.20
Purchase #6	$41.61	5.700%	$43.9818	$43.98	$44.00	$44.00
Purchase #7	$7.35	6.699%	$7.8424	$7.84	$7.85	$7.80
7 purchase totals =	$372.44		$403.8547	$403.85	$403.90	$403.90