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	$79.60	13.147%	$90.065	$90.07	$90.05	$90.10
Purchase #2	$31.50	11.468%	$35.1124	$35.11	$35.10	$35.10
Purchase #3	$32.30	4.628%	$33.7948	$33.79	$33.80	$33.80
Purchase #4	$55.29	12.832%	$62.3848	$62.38	$62.40	$62.40
Purchase #5	$148.57	9.481%	$162.6559	$162.66	$162.65	$162.70
Purchase #6	$242.59	11.464%	$270.4005	$270.40	$270.40	$270.40
Purchase #7	$25.36	6.493%	$27.0066	$27.01	$27.00	$27.00
7 purchase totals =	$615.21		$681.4200	$681.42	$681.40	$681.50