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	$17.60	7.336%	$18.8911	$18.89	$18.90	$18.90
Purchase #2	$57.25	4.690%	$59.935	$59.94	$59.95	$59.90
Purchase #3	$131.67	13.410%	$149.3269	$149.33	$149.35	$149.30
Purchase #4	$43.66	8.643%	$47.4335	$47.43	$47.45	$47.40
Purchase #5	$231.48	13.736%	$263.2761	$263.28	$263.30	$263.30
Purchase #6	$70.83	3.482%	$73.2963	$73.30	$73.30	$73.30
Purchase #7	$76.71	7.666%	$82.5906	$82.59	$82.60	$82.60
7 purchase totals =	$629.20		$694.7495	$694.76	$694.85	$694.70