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	$29.29	12.245%	$32.8766	$32.88	$32.90	$32.90
Purchase #2	$128.72	10.276%	$141.9473	$141.95	$141.95	$141.90
Purchase #3	$218.43	11.228%	$242.9553	$242.96	$242.95	$243.00
Purchase #4	$109.79	10.177%	$120.9633	$120.96	$120.95	$121.00
Purchase #5	$56.48	13.427%	$64.0636	$64.06	$64.05	$64.10
Purchase #6	$153.74	12.479%	$172.9252	$172.93	$172.95	$172.90
Purchase #7	$11.82	4.426%	$12.3432	$12.34	$12.35	$12.30
7 purchase totals =	$708.27		$788.0745	$788.08	$788.10	$788.10