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	$79.61	5.382%	$83.8946	$83.89	$83.90	$83.90
Purchase #2	$199.38	10.266%	$219.8484	$219.85	$219.85	$219.80
Purchase #3	$76.54	12.111%	$85.8098	$85.81	$85.80	$85.80
Purchase #4	$217.33	9.683%	$238.3741	$238.37	$238.35	$238.40
Purchase #5	$225.79	8.762%	$245.5737	$245.57	$245.55	$245.60
Purchase #6	$52.79	10.655%	$58.4148	$58.41	$58.40	$58.40
Purchase #7	$240.38	10.294%	$265.1247	$265.12	$265.10	$265.10
7 purchase totals =	$1,091.82		$1,197.0401	$1,197.02	$1,196.95	$1,197.00