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	$86.45	5.277%	$91.012	$91.01	$91.00	$91.00
Purchase #2	$228.25	9.664%	$250.3081	$250.31	$250.30	$250.30
Purchase #3	$145.79	13.552%	$165.5475	$165.55	$165.55	$165.50
Purchase #4	$159.52	7.752%	$171.886	$171.89	$171.90	$171.90
Purchase #5	$91.92	6.789%	$98.1604	$98.16	$98.15	$98.20
Purchase #6	$136.87	6.178%	$145.3258	$145.33	$145.35	$145.30
Purchase #7	$187.32	10.310%	$206.6327	$206.63	$206.65	$206.60
7 purchase totals =	$1,036.12		$1,128.8725	$1,128.88	$1,128.90	$1,128.80