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	$20.94	6.347%	$22.2691	$22.27	$22.25	$22.30
Purchase #2	$110.64	7.761%	$119.2268	$119.23	$119.25	$119.20
Purchase #3	$189.99	3.240%	$196.1457	$196.15	$196.15	$196.10
Purchase #4	$151.40	13.614%	$172.0116	$172.01	$172.00	$172.00
Purchase #5	$40.80	3.514%	$42.2337	$42.23	$42.25	$42.20
Purchase #6	$226.82	7.331%	$243.4482	$243.45	$243.45	$243.40
Purchase #7	$185.90	8.160%	$201.0694	$201.07	$201.05	$201.10
7 purchase totals =	$926.49		$996.4045	$996.41	$996.40	$996.30