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	$94.96	3.308%	$98.1013	$98.10	$98.10	$98.10
Purchase #2	$186.63	5.203%	$196.3404	$196.34	$196.35	$196.30
Purchase #3	$151.41	13.262%	$171.49	$171.49	$171.50	$171.50
Purchase #4	$91.70	4.234%	$95.5826	$95.58	$95.60	$95.60
Purchase #5	$31.50	3.445%	$32.5852	$32.59	$32.60	$32.60
Purchase #6	$37.50	9.755%	$41.1581	$41.16	$41.15	$41.20
Purchase #7	$245.86	13.573%	$279.2306	$279.23	$279.25	$279.20
7 purchase totals =	$839.56		$914.4882	$914.49	$914.55	$914.50