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	$51.62	12.793%	$58.2237	$58.22	$58.20	$58.20
Purchase #2	$35.37	13.459%	$40.1304	$40.13	$40.15	$40.10
Purchase #3	$114.62	11.507%	$127.8093	$127.81	$127.80	$127.80
Purchase #4	$6.64	11.686%	$7.416	$7.42	$7.40	$7.40
Purchase #5	$36.28	12.579%	$40.8437	$40.84	$40.85	$40.80
Purchase #6	$135.37	6.298%	$143.8956	$143.90	$143.90	$143.90
Purchase #7	$83.48	7.394%	$89.6525	$89.65	$89.65	$89.70
7 purchase totals =	$463.38		$507.9712	$507.97	$507.95	$507.90