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	$50.89	8.337%	$55.1327	$55.13	$55.15	$55.10
Purchase #2	$119.97	6.340%	$127.5761	$127.58	$127.60	$127.60
Purchase #3	$234.86	6.532%	$250.2011	$250.20	$250.20	$250.20
Purchase #4	$33.88	5.102%	$35.6086	$35.61	$35.60	$35.60
Purchase #5	$69.92	11.569%	$78.009	$78.01	$78.00	$78.00
Purchase #6	$243.57	12.780%	$274.6982	$274.70	$274.70	$274.70
Purchase #7	$71.35	11.538%	$79.5824	$79.58	$79.60	$79.60
7 purchase totals =	$824.44		$900.8081	$900.81	$900.85	$900.80