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	$39.31	8.844%	$42.7866	$42.79	$42.80	$42.80
Purchase #2	$250.97	9.754%	$275.4496	$275.45	$275.45	$275.40
Purchase #3	$187.54	11.786%	$209.6435	$209.64	$209.65	$209.60
Purchase #4	$41.80	6.351%	$44.4547	$44.45	$44.45	$44.50
Purchase #5	$27.41	5.378%	$28.8841	$28.88	$28.90	$28.90
Purchase #6	$181.86	7.790%	$196.0269	$196.03	$196.05	$196.00
Purchase #7	$201.66	7.127%	$216.0323	$216.03	$216.05	$216.00
7 purchase totals =	$930.55		$1,013.2777	$1,013.27	$1,013.35	$1,013.20