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	$120.59	9.339%	$131.8519	$131.85	$131.85	$131.90
Purchase #2	$216.73	12.185%	$243.1386	$243.14	$243.15	$243.10
Purchase #3	$110.65	9.218%	$120.8497	$120.85	$120.85	$120.80
Purchase #4	$41.80	7.822%	$45.0696	$45.07	$45.05	$45.10
Purchase #5	$194.77	7.820%	$210.001	$210.00	$210.00	$210.00
Purchase #6	$245.77	10.502%	$271.5808	$271.58	$271.60	$271.60
Purchase #7	$213.85	12.183%	$239.9033	$239.90	$239.90	$239.90
7 purchase totals =	$1,144.16		$1,262.3949	$1,262.39	$1,262.40	$1,262.40