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	$45.39	3.378%	$46.9233	$46.92	$46.90	$46.90
Purchase #2	$192.83	10.655%	$213.376	$213.38	$213.40	$213.40
Purchase #3	$136.93	8.693%	$148.8333	$148.83	$148.85	$148.80
Purchase #4	$212.57	5.122%	$223.4578	$223.46	$223.45	$223.50
Purchase #5	$39.33	7.310%	$42.205	$42.21	$42.20	$42.20
Purchase #6	$90.94	6.503%	$96.8538	$96.85	$96.85	$96.90
Purchase #7	$99.57	5.376%	$104.9229	$104.92	$104.90	$104.90
7 purchase totals =	$817.56		$876.5721	$876.57	$876.55	$876.60