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	$134.26	3.851%	$139.4304	$139.43	$139.45	$139.40
Purchase #2	$40.37	8.805%	$43.9246	$43.92	$43.90	$43.90
Purchase #3	$136.26	10.362%	$150.3793	$150.38	$150.40	$150.40
Purchase #4	$128.73	10.721%	$142.5311	$142.53	$142.55	$142.50
Purchase #5	$73.50	12.830%	$82.9301	$82.93	$82.95	$82.90
Purchase #6	$165.78	7.189%	$177.6979	$177.70	$177.70	$177.70
Purchase #7	$93.93	12.789%	$105.9427	$105.94	$105.95	$105.90
7 purchase totals =	$772.83		$842.8361	$842.83	$842.90	$842.70