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	$74.83	4.820%	$78.4368	$78.44	$78.45	$78.40
Purchase #2	$212.33	12.448%	$238.7608	$238.76	$238.75	$238.80
Purchase #3	$246.75	8.332%	$267.3092	$267.31	$267.30	$267.30
Purchase #4	$41.96	3.387%	$43.3812	$43.38	$43.40	$43.40
Purchase #5	$249.55	9.127%	$272.3264	$272.33	$272.35	$272.30
Purchase #6	$120.64	6.870%	$128.928	$128.93	$128.95	$128.90
Purchase #7	$201.50	7.578%	$216.7697	$216.77	$216.75	$216.80
7 purchase totals =	$1,147.56		$1,245.9121	$1,245.92	$1,245.95	$1,245.90