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	$199.31	8.373%	$215.9982	$216.00	$216.00	$216.00
Purchase #2	$189.86	10.359%	$209.5276	$209.53	$209.55	$209.50
Purchase #3	$137.78	9.171%	$150.4158	$150.42	$150.40	$150.40
Purchase #4	$127.29	9.411%	$139.2693	$139.27	$139.25	$139.30
Purchase #5	$199.37	8.809%	$216.9325	$216.93	$216.95	$216.90
Purchase #6	$37.47	13.194%	$42.4138	$42.41	$42.40	$42.40
Purchase #7	$27.66	10.117%	$30.4584	$30.46	$30.45	$30.50
7 purchase totals =	$918.74		$1,005.0156	$1,005.02	$1,005.00	$1,005.00