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	$109.77	3.325%	$113.4199	$113.42	$113.40	$113.40
Purchase #2	$196.42	11.683%	$219.3677	$219.37	$219.35	$219.40
Purchase #3	$61.67	8.279%	$66.7757	$66.78	$66.80	$66.80
Purchase #4	$180.87	3.572%	$187.3307	$187.33	$187.35	$187.30
Purchase #5	$73.92	11.200%	$82.199	$82.20	$82.20	$82.20
Purchase #6	$166.25	12.138%	$186.4294	$186.43	$186.45	$186.40
Purchase #7	$37.34	10.825%	$41.3821	$41.38	$41.40	$41.40
7 purchase totals =	$826.24		$896.9045	$896.91	$896.95	$896.90