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	$139.68	5.208%	$146.9545	$146.95	$146.95	$147.00
Purchase #2	$56.42	13.220%	$63.8787	$63.88	$63.90	$63.90
Purchase #3	$31.78	3.578%	$32.9171	$32.92	$32.90	$32.90
Purchase #4	$143.87	11.809%	$160.8596	$160.86	$160.85	$160.90
Purchase #5	$189.77	10.143%	$209.0184	$209.02	$209.00	$209.00
Purchase #6	$85.55	6.767%	$91.3392	$91.34	$91.35	$91.30
Purchase #7	$65.93	8.696%	$71.6633	$71.66	$71.65	$71.70
7 purchase totals =	$713.00		$776.6308	$776.63	$776.60	$776.70