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	$226.94	4.129%	$236.3104	$236.31	$236.30	$236.30
Purchase #2	$170.91	13.475%	$193.9401	$193.94	$193.95	$193.90
Purchase #3	$79.34	12.557%	$89.3027	$89.30	$89.30	$89.30
Purchase #4	$185.73	12.693%	$209.3047	$209.30	$209.30	$209.30
Purchase #5	$39.39	3.808%	$40.89	$40.89	$40.90	$40.90
Purchase #6	$213.91	9.199%	$233.5876	$233.59	$233.60	$233.60
Purchase #7	$86.43	11.540%	$96.404	$96.40	$96.40	$96.40
7 purchase totals =	$1,002.65		$1,099.7395	$1,099.73	$1,099.75	$1,099.70