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	$105.81	11.341%	$117.8099	$117.81	$117.80	$117.80
Purchase #2	$99.85	3.478%	$103.3228	$103.32	$103.30	$103.30
Purchase #3	$101.94	11.807%	$113.9761	$113.98	$114.00	$114.00
Purchase #4	$61.61	9.597%	$67.5227	$67.52	$67.50	$67.50
Purchase #5	$34.27	3.690%	$35.5346	$35.53	$35.55	$35.50
Purchase #6	$88.57	9.421%	$96.9142	$96.91	$96.90	$96.90
Purchase #7	$119.30	8.850%	$129.8581	$129.86	$129.85	$129.90
7 purchase totals =	$611.35		$664.9384	$664.93	$664.90	$664.90