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	$179.67	5.110%	$188.8511	$188.85	$188.85	$188.90
Purchase #2	$250.48	3.218%	$258.5404	$258.54	$258.55	$258.50
Purchase #3	$123.40	12.591%	$138.9373	$138.94	$138.95	$138.90
Purchase #4	$54.36	9.116%	$59.3155	$59.32	$59.30	$59.30
Purchase #5	$175.56	10.811%	$194.5398	$194.54	$194.55	$194.50
Purchase #6	$43.76	7.167%	$46.8963	$46.90	$46.90	$46.90
Purchase #7	$240.43	8.310%	$260.4097	$260.41	$260.40	$260.40
7 purchase totals =	$1,067.66		$1,147.4901	$1,147.50	$1,147.50	$1,147.40