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	$80.76	7.633%	$86.9244	$86.92	$86.90	$86.90
Purchase #2	$121.50	5.659%	$128.3757	$128.38	$128.40	$128.40
Purchase #3	$54.33	13.168%	$61.4842	$61.48	$61.50	$61.50
Purchase #4	$115.67	7.300%	$124.1139	$124.11	$124.10	$124.10
Purchase #5	$33.73	13.782%	$38.3787	$38.38	$38.40	$38.40
Purchase #6	$187.92	13.618%	$213.5109	$213.51	$213.50	$213.50
Purchase #7	$98.89	12.343%	$111.096	$111.10	$111.10	$111.10
7 purchase totals =	$692.80		$763.8838	$763.88	$763.90	$763.90