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	$46.54	6.648%	$49.634	$49.63	$49.65	$49.60
Purchase #2	$120.68	3.114%	$124.438	$124.44	$124.45	$124.40
Purchase #3	$35.59	10.661%	$39.3842	$39.38	$39.40	$39.40
Purchase #4	$86.80	3.194%	$89.5724	$89.57	$89.55	$89.60
Purchase #5	$233.90	4.264%	$243.8735	$243.87	$243.85	$243.90
Purchase #6	$199.48	4.718%	$208.8915	$208.89	$208.90	$208.90
Purchase #7	$30.70	8.774%	$33.3936	$33.39	$33.40	$33.40
7 purchase totals =	$753.69		$789.1872	$789.17	$789.20	$789.20