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	$189.54	12.321%	$212.8932	$212.89	$212.90	$212.90
Purchase #2	$31.39	12.118%	$35.1938	$35.19	$35.20	$35.20
Purchase #3	$153.98	4.470%	$160.8629	$160.86	$160.85	$160.90
Purchase #4	$95.29	4.394%	$99.477	$99.48	$99.50	$99.50
Purchase #5	$20.31	10.192%	$22.38	$22.38	$22.40	$22.40
Purchase #6	$85.88	5.266%	$90.4024	$90.40	$90.40	$90.40
Purchase #7	$236.36	10.773%	$261.8231	$261.82	$261.80	$261.80
7 purchase totals =	$812.75		$883.0324	$883.02	$883.05	$883.10