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	$143.55	5.601%	$151.5902	$151.59	$151.60	$151.60
Purchase #2	$124.53	5.407%	$131.2633	$131.26	$131.25	$131.30
Purchase #3	$243.97	10.625%	$269.8918	$269.89	$269.90	$269.90
Purchase #4	$88.50	6.455%	$94.2127	$94.21	$94.20	$94.20
Purchase #5	$89.82	10.127%	$98.9161	$98.92	$98.90	$98.90
Purchase #6	$22.71	12.736%	$25.6023	$25.60	$25.60	$25.60
Purchase #7	$63.26	11.833%	$70.7456	$70.75	$70.75	$70.70
7 purchase totals =	$776.34		$842.2220	$842.22	$842.20	$842.20