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	$83.98	7.116%	$89.956	$89.96	$89.95	$90.00
Purchase #2	$110.87	5.165%	$116.5964	$116.60	$116.60	$116.60
Purchase #3	$97.68	11.483%	$108.8966	$108.90	$108.90	$108.90
Purchase #4	$24.95	9.775%	$27.3889	$27.39	$27.40	$27.40
Purchase #5	$55.67	7.606%	$59.9043	$59.90	$59.90	$59.90
Purchase #6	$203.66	4.637%	$213.1037	$213.10	$213.10	$213.10
Purchase #7	$55.85	3.181%	$57.6266	$57.63	$57.65	$57.60
7 purchase totals =	$632.66		$673.4725	$673.48	$673.50	$673.50