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	$36.80	4.539%	$38.4704	$38.47	$38.45	$38.50
Purchase #2	$179.46	9.594%	$196.6774	$196.68	$196.70	$196.70
Purchase #3	$131.71	3.645%	$136.5108	$136.51	$136.50	$136.50
Purchase #4	$61.84	11.107%	$68.7086	$68.71	$68.70	$68.70
Purchase #5	$206.46	7.541%	$222.0291	$222.03	$222.05	$222.00
Purchase #6	$52.59	7.868%	$56.7278	$56.73	$56.75	$56.70
Purchase #7	$113.47	13.591%	$128.8917	$128.89	$128.90	$128.90
7 purchase totals =	$782.33		$848.0158	$848.02	$848.05	$848.00