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	$30.93	4.706%	$32.3856	$32.39	$32.40	$32.40
Purchase #2	$168.78	11.653%	$188.4479	$188.45	$188.45	$188.40
Purchase #3	$19.69	10.605%	$21.7781	$21.78	$21.80	$21.80
Purchase #4	$95.95	8.165%	$103.7843	$103.78	$103.80	$103.80
Purchase #5	$178.27	9.155%	$194.5906	$194.59	$194.60	$194.60
Purchase #6	$22.60	11.386%	$25.1732	$25.17	$25.15	$25.20
Purchase #7	$250.33	3.741%	$259.6948	$259.69	$259.70	$259.70
7 purchase totals =	$766.55		$825.8545	$825.85	$825.90	$825.90