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	$127.26	10.238%	$140.2889	$140.29	$140.30	$140.30
Purchase #2	$115.50	6.500%	$123.0075	$123.01	$123.00	$123.00
Purchase #3	$237.82	3.171%	$245.3613	$245.36	$245.35	$245.40
Purchase #4	$41.30	10.204%	$45.5143	$45.51	$45.50	$45.50
Purchase #5	$53.31	3.839%	$55.3566	$55.36	$55.35	$55.40
Purchase #6	$192.85	10.535%	$213.1667	$213.17	$213.15	$213.20
Purchase #7	$6.91	10.798%	$7.6561	$7.66	$7.65	$7.70
7 purchase totals =	$774.95		$830.3514	$830.36	$830.30	$830.50