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	$35.45	13.743%	$40.3219	$40.32	$40.30	$40.30
Purchase #2	$69.62	11.850%	$77.87	$77.87	$77.85	$77.90
Purchase #3	$223.37	11.673%	$249.444	$249.44	$249.45	$249.40
Purchase #4	$6.42	11.712%	$7.1719	$7.17	$7.15	$7.20
Purchase #5	$81.32	5.494%	$85.7877	$85.79	$85.80	$85.80
Purchase #6	$34.64	6.808%	$36.9983	$37.00	$37.00	$37.00
Purchase #7	$202.69	4.755%	$212.3279	$212.33	$212.35	$212.30
7 purchase totals =	$653.51		$709.9217	$709.92	$709.90	$709.90