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	$78.42	13.635%	$89.1126	$89.11	$89.10	$89.10
Purchase #2	$59.92	11.805%	$66.9936	$66.99	$67.00	$67.00
Purchase #3	$73.54	12.502%	$82.734	$82.73	$82.75	$82.70
Purchase #4	$216.80	7.741%	$233.5825	$233.58	$233.60	$233.60
Purchase #5	$168.25	3.557%	$174.2347	$174.23	$174.25	$174.20
Purchase #6	$205.86	11.172%	$228.8587	$228.86	$228.85	$228.90
Purchase #7	$86.88	7.539%	$93.4299	$93.43	$93.45	$93.40
7 purchase totals =	$889.67		$968.9460	$968.93	$969.00	$968.90