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	$236.31	5.452%	$249.1936	$249.19	$249.20	$249.20
Purchase #2	$121.56	5.797%	$128.6068	$128.61	$128.60	$128.60
Purchase #3	$152.53	5.777%	$161.3417	$161.34	$161.35	$161.30
Purchase #4	$249.91	12.803%	$281.906	$281.91	$281.90	$281.90
Purchase #5	$156.91	9.106%	$171.1982	$171.20	$171.20	$171.20
Purchase #6	$9.69	7.180%	$10.3857	$10.39	$10.40	$10.40
Purchase #7	$83.91	7.648%	$90.3274	$90.33	$90.35	$90.30
7 purchase totals =	$1,010.82		$1,092.9594	$1,092.97	$1,093.00	$1,092.90