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	$250.82	9.691%	$275.127	$275.13	$275.15	$275.10
Purchase #2	$125.84	4.810%	$131.8929	$131.89	$131.90	$131.90
Purchase #3	$81.60	10.502%	$90.1696	$90.17	$90.15	$90.20
Purchase #4	$196.87	9.373%	$215.3226	$215.32	$215.30	$215.30
Purchase #5	$31.97	3.315%	$33.0298	$33.03	$33.05	$33.00
Purchase #6	$173.48	8.838%	$188.8122	$188.81	$188.80	$188.80
Purchase #7	$243.90	10.127%	$268.5998	$268.60	$268.60	$268.60
7 purchase totals =	$1,104.48		$1,202.9539	$1,202.95	$1,202.95	$1,202.90