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	$121.59	9.177%	$132.7483	$132.75	$132.75	$132.70
Purchase #2	$35.26	5.440%	$37.1781	$37.18	$37.20	$37.20
Purchase #3	$72.72	3.863%	$75.5292	$75.53	$75.55	$75.50
Purchase #4	$154.59	9.201%	$168.8138	$168.81	$168.80	$168.80
Purchase #5	$216.35	3.147%	$223.1585	$223.16	$223.15	$223.20
Purchase #6	$141.40	6.318%	$150.3337	$150.33	$150.35	$150.30
Purchase #7	$119.25	10.143%	$131.3455	$131.35	$131.35	$131.30
7 purchase totals =	$861.16		$919.1071	$919.11	$919.15	$919.00