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	$125.33	3.246%	$129.3982	$129.40	$129.40	$129.40
Purchase #2	$118.81	4.654%	$124.3394	$124.34	$124.35	$124.30
Purchase #3	$123.76	6.115%	$131.3279	$131.33	$131.35	$131.30
Purchase #4	$169.58	7.552%	$182.3867	$182.39	$182.40	$182.40
Purchase #5	$76.49	8.226%	$82.7821	$82.78	$82.80	$82.80
Purchase #6	$81.89	8.159%	$88.5714	$88.57	$88.55	$88.60
Purchase #7	$42.98	6.409%	$45.7346	$45.73	$45.75	$45.70
7 purchase totals =	$738.84		$784.5403	$784.54	$784.60	$784.50