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	$190.55	10.287%	$210.1519	$210.15	$210.15	$210.20
Purchase #2	$86.28	3.793%	$89.5526	$89.55	$89.55	$89.60
Purchase #3	$31.34	11.695%	$35.0052	$35.01	$35.00	$35.00
Purchase #4	$63.42	12.166%	$71.1357	$71.14	$71.15	$71.10
Purchase #5	$120.43	6.663%	$128.4543	$128.45	$128.45	$128.50
Purchase #6	$124.60	5.763%	$131.7807	$131.78	$131.80	$131.80
Purchase #7	$150.40	13.573%	$170.8138	$170.81	$170.80	$170.80
7 purchase totals =	$767.02		$836.8942	$836.89	$836.90	$837.00