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	$28.25	13.152%	$31.9654	$31.97	$31.95	$32.00
Purchase #2	$17.92	12.102%	$20.0887	$20.09	$20.10	$20.10
Purchase #3	$218.89	7.277%	$234.8186	$234.82	$234.80	$234.80
Purchase #4	$240.39	12.538%	$270.5301	$270.53	$270.55	$270.50
Purchase #5	$225.80	5.143%	$237.4129	$237.41	$237.40	$237.40
Purchase #6	$179.79	9.424%	$196.7334	$196.73	$196.75	$196.70
Purchase #7	$165.29	11.273%	$183.9231	$183.92	$183.90	$183.90
7 purchase totals =	$1,076.33		$1,175.4722	$1,175.47	$1,175.45	$1,175.40