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	$37.56	4.467%	$39.2378	$39.24	$39.25	$39.20
Purchase #2	$182.83	7.109%	$195.8274	$195.83	$195.85	$195.80
Purchase #3	$91.31	7.861%	$98.4879	$98.49	$98.50	$98.50
Purchase #4	$52.78	5.224%	$55.5372	$55.54	$55.55	$55.50
Purchase #5	$15.85	13.850%	$18.0452	$18.05	$18.05	$18.00
Purchase #6	$225.57	5.642%	$238.2967	$238.30	$238.30	$238.30
Purchase #7	$79.88	7.383%	$85.7775	$85.78	$85.80	$85.80
7 purchase totals =	$685.78		$731.2097	$731.23	$731.30	$731.10