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	$239.37	3.776%	$248.4086	$248.41	$248.40	$248.40
Purchase #2	$216.84	13.133%	$245.3176	$245.32	$245.30	$245.30
Purchase #3	$248.67	7.874%	$268.2503	$268.25	$268.25	$268.30
Purchase #4	$73.67	11.655%	$82.2562	$82.26	$82.25	$82.30
Purchase #5	$111.49	7.510%	$119.8629	$119.86	$119.85	$119.90
Purchase #6	$103.38	5.409%	$108.9718	$108.97	$108.95	$109.00
Purchase #7	$72.54	3.137%	$74.8156	$74.82	$74.80	$74.80
7 purchase totals =	$1,065.96		$1,147.8830	$1,147.89	$1,147.80	$1,148.00