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	$22.29	11.607%	$24.8772	$24.88	$24.90	$24.90
Purchase #2	$164.50	13.387%	$186.5216	$186.52	$186.50	$186.50
Purchase #3	$90.35	11.718%	$100.9372	$100.94	$100.95	$100.90
Purchase #4	$179.82	3.175%	$185.5293	$185.53	$185.55	$185.50
Purchase #5	$54.38	9.675%	$59.6413	$59.64	$59.65	$59.60
Purchase #6	$88.34	12.179%	$99.0989	$99.10	$99.10	$99.10
Purchase #7	$184.37	8.359%	$199.7815	$199.78	$199.80	$199.80
7 purchase totals =	$784.05		$856.3870	$856.39	$856.45	$856.30