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	$80.55	12.819%	$90.8757	$90.88	$90.90	$90.90
Purchase #2	$239.50	3.249%	$247.2814	$247.28	$247.30	$247.30
Purchase #3	$182.48	11.548%	$203.5528	$203.55	$203.55	$203.60
Purchase #4	$33.95	12.436%	$38.172	$38.17	$38.15	$38.20
Purchase #5	$33.63	12.611%	$37.8711	$37.87	$37.85	$37.90
Purchase #6	$43.69	4.269%	$45.5551	$45.56	$45.55	$45.60
Purchase #7	$210.57	6.315%	$223.8675	$223.87	$223.85	$223.90
7 purchase totals =	$824.37		$887.1756	$887.18	$887.15	$887.40