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	$83.25	7.514%	$89.5054	$89.51	$89.50	$89.50
Purchase #2	$99.38	5.386%	$104.7326	$104.73	$104.75	$104.70
Purchase #3	$216.49	3.696%	$224.4915	$224.49	$224.50	$224.50
Purchase #4	$148.32	12.843%	$167.3687	$167.37	$167.35	$167.40
Purchase #5	$246.98	13.419%	$280.1222	$280.12	$280.10	$280.10
Purchase #6	$8.40	5.615%	$8.8717	$8.87	$8.85	$8.90
Purchase #7	$24.55	13.154%	$27.7793	$27.78	$27.80	$27.80
7 purchase totals =	$827.37		$902.8714	$902.87	$902.85	$902.90