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	$224.72	11.390%	$250.3156	$250.32	$250.30	$250.30
Purchase #2	$6.36	12.197%	$7.1357	$7.14	$7.15	$7.10
Purchase #3	$152.76	12.521%	$171.8871	$171.89	$171.90	$171.90
Purchase #4	$55.65	11.559%	$62.0826	$62.08	$62.10	$62.10
Purchase #5	$120.29	6.796%	$128.4649	$128.46	$128.45	$128.50
Purchase #6	$179.89	5.811%	$190.3434	$190.34	$190.35	$190.30
Purchase #7	$94.42	5.833%	$99.9275	$99.93	$99.95	$99.90
7 purchase totals =	$834.09		$910.1568	$910.16	$910.20	$910.10