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	$240.59	12.561%	$270.8105	$270.81	$270.80	$270.80
Purchase #2	$59.30	12.526%	$66.7279	$66.73	$66.75	$66.70
Purchase #3	$67.31	8.606%	$73.1027	$73.10	$73.10	$73.10
Purchase #4	$181.83	4.545%	$190.0942	$190.09	$190.10	$190.10
Purchase #5	$78.69	8.359%	$85.2677	$85.27	$85.25	$85.30
Purchase #6	$165.64	7.146%	$177.4766	$177.48	$177.50	$177.50
Purchase #7	$209.92	6.602%	$223.7789	$223.78	$223.80	$223.80
7 purchase totals =	$1,003.28		$1,087.2585	$1,087.26	$1,087.30	$1,087.30