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	$80.71	10.149%	$88.9013	$88.90	$88.90	$88.90
Purchase #2	$189.53	7.751%	$204.2205	$204.22	$204.20	$204.20
Purchase #3	$34.44	3.238%	$35.5552	$35.56	$35.55	$35.60
Purchase #4	$82.35	8.471%	$89.3259	$89.33	$89.35	$89.30
Purchase #5	$134.37	9.417%	$147.0236	$147.02	$147.00	$147.00
Purchase #6	$112.60	7.114%	$120.6104	$120.61	$120.60	$120.60
Purchase #7	$216.83	13.275%	$245.6142	$245.61	$245.60	$245.60
7 purchase totals =	$850.83		$931.2511	$931.25	$931.20	$931.20