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	$18.98	12.515%	$21.3553	$21.36	$21.35	$21.40
Purchase #2	$242.89	13.365%	$275.3522	$275.35	$275.35	$275.40
Purchase #3	$98.83	10.131%	$108.8425	$108.84	$108.85	$108.80
Purchase #4	$51.69	8.290%	$55.9751	$55.98	$56.00	$56.00
Purchase #5	$217.86	11.210%	$242.2821	$242.28	$242.30	$242.30
Purchase #6	$240.76	9.353%	$263.2783	$263.28	$263.30	$263.30
Purchase #7	$41.96	4.574%	$43.8793	$43.88	$43.90	$43.90
7 purchase totals =	$912.97		$1,010.9648	$1,010.97	$1,011.05	$1,011.10