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	$30.76	5.586%	$32.4783	$32.48	$32.50	$32.50
Purchase #2	$61.48	12.638%	$69.2498	$69.25	$69.25	$69.20
Purchase #3	$200.83	4.538%	$209.9437	$209.94	$209.95	$209.90
Purchase #4	$196.77	3.805%	$204.2571	$204.26	$204.25	$204.30
Purchase #5	$70.73	10.425%	$78.1036	$78.10	$78.10	$78.10
Purchase #6	$35.74	5.706%	$37.7793	$37.78	$37.80	$37.80
Purchase #7	$40.59	11.699%	$45.3386	$45.34	$45.35	$45.30
7 purchase totals =	$636.90		$677.1504	$677.15	$677.20	$677.10