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	$31.57	11.853%	$35.312	$35.31	$35.30	$35.30
Purchase #2	$57.76	8.310%	$62.5599	$62.56	$62.55	$62.60
Purchase #3	$204.91	5.129%	$215.4198	$215.42	$215.40	$215.40
Purchase #4	$211.73	5.321%	$222.9962	$223.00	$223.00	$223.00
Purchase #5	$42.25	6.717%	$45.0879	$45.09	$45.10	$45.10
Purchase #6	$239.88	10.748%	$265.6623	$265.66	$265.65	$265.70
Purchase #7	$82.62	6.811%	$88.2472	$88.25	$88.25	$88.20
7 purchase totals =	$870.72		$935.2853	$935.29	$935.25	$935.30