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	$89.34	6.138%	$94.8237	$94.82	$94.80	$94.80
Purchase #2	$249.89	11.584%	$278.8373	$278.84	$278.85	$278.80
Purchase #3	$7.46	5.259%	$7.8523	$7.85	$7.85	$7.90
Purchase #4	$96.43	11.301%	$107.3276	$107.33	$107.35	$107.30
Purchase #5	$203.52	4.709%	$213.1038	$213.10	$213.10	$213.10
Purchase #6	$220.50	12.516%	$248.0978	$248.10	$248.10	$248.10
Purchase #7	$141.52	4.712%	$148.1884	$148.19	$148.20	$148.20
7 purchase totals =	$1,008.66		$1,098.2309	$1,098.23	$1,098.25	$1,098.20