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	$162.43	12.391%	$182.5567	$182.56	$182.55	$182.60
Purchase #2	$124.48	7.562%	$133.8932	$133.89	$133.90	$133.90
Purchase #3	$139.36	12.116%	$156.2449	$156.24	$156.25	$156.20
Purchase #4	$85.88	13.130%	$97.156	$97.16	$97.15	$97.20
Purchase #5	$162.42	10.496%	$179.4676	$179.47	$179.45	$179.50
Purchase #6	$201.55	7.761%	$217.1923	$217.19	$217.20	$217.20
Purchase #7	$12.70	9.402%	$13.8941	$13.89	$13.90	$13.90
7 purchase totals =	$888.82		$980.4048	$980.40	$980.40	$980.50