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	$32.83	8.231%	$35.5322	$35.53	$35.55	$35.50
Purchase #2	$38.66	10.385%	$42.6748	$42.67	$42.65	$42.70
Purchase #3	$57.29	8.483%	$62.1499	$62.15	$62.15	$62.10
Purchase #4	$62.65	11.661%	$69.9556	$69.96	$69.95	$70.00
Purchase #5	$79.79	11.576%	$89.0265	$89.03	$89.05	$89.00
Purchase #6	$149.29	11.445%	$166.3762	$166.38	$166.40	$166.40
Purchase #7	$133.48	4.360%	$139.2997	$139.30	$139.30	$139.30
7 purchase totals =	$553.99		$605.0149	$605.02	$605.05	$605.00