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	$181.31	5.339%	$190.9901	$190.99	$191.00	$191.00
Purchase #2	$212.30	8.268%	$229.853	$229.85	$229.85	$229.90
Purchase #3	$159.41	4.455%	$166.5117	$166.51	$166.50	$166.50
Purchase #4	$191.79	3.484%	$198.472	$198.47	$198.45	$198.50
Purchase #5	$212.28	4.718%	$222.2954	$222.30	$222.30	$222.30
Purchase #6	$108.82	7.270%	$116.7312	$116.73	$116.75	$116.70
Purchase #7	$246.68	11.468%	$274.9693	$274.97	$274.95	$275.00
7 purchase totals =	$1,312.59		$1,399.8227	$1,399.82	$1,399.80	$1,399.90