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	$5.82	7.721%	$6.2694	$6.27	$6.25	$6.30
Purchase #2	$86.84	4.652%	$90.8798	$90.88	$90.90	$90.90
Purchase #3	$201.96	11.803%	$225.7973	$225.80	$225.80	$225.80
Purchase #4	$31.44	11.462%	$35.0437	$35.04	$35.05	$35.00
Purchase #5	$187.60	11.561%	$209.2884	$209.29	$209.30	$209.30
Purchase #6	$204.89	8.610%	$222.531	$222.53	$222.55	$222.50
Purchase #7	$114.62	3.400%	$118.5171	$118.52	$118.50	$118.50
7 purchase totals =	$833.17		$908.3267	$908.33	$908.35	$908.30