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	$28.69	9.183%	$31.3246	$31.32	$31.30	$31.30
Purchase #2	$187.94	6.589%	$200.3234	$200.32	$200.30	$200.30
Purchase #3	$134.86	4.723%	$141.2294	$141.23	$141.25	$141.20
Purchase #4	$243.66	7.112%	$260.9891	$260.99	$261.00	$261.00
Purchase #5	$234.97	3.615%	$243.4642	$243.46	$243.45	$243.50
Purchase #6	$134.69	12.596%	$151.6556	$151.66	$151.65	$151.70
Purchase #7	$179.59	6.860%	$191.9099	$191.91	$191.90	$191.90
7 purchase totals =	$1,144.40		$1,220.8962	$1,220.89	$1,220.85	$1,220.90