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	$31.61	6.712%	$33.7317	$33.73	$33.75	$33.70
Purchase #2	$80.54	10.513%	$89.0072	$89.01	$89.00	$89.00
Purchase #3	$245.88	7.437%	$264.1661	$264.17	$264.15	$264.20
Purchase #4	$81.85	4.822%	$85.7968	$85.80	$85.80	$85.80
Purchase #5	$70.25	6.454%	$74.7839	$74.78	$74.80	$74.80
Purchase #6	$73.50	13.543%	$83.4541	$83.45	$83.45	$83.50
Purchase #7	$144.90	7.775%	$156.166	$156.17	$156.15	$156.20
7 purchase totals =	$728.53		$787.1058	$787.11	$787.10	$787.20