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	$78.47	8.807%	$85.3809	$85.38	$85.40	$85.40
Purchase #2	$131.82	6.454%	$140.3277	$140.33	$140.35	$140.30
Purchase #3	$31.96	11.376%	$35.5958	$35.60	$35.60	$35.60
Purchase #4	$65.85	6.454%	$70.1	$70.10	$70.10	$70.10
Purchase #5	$182.53	11.525%	$203.5666	$203.57	$203.55	$203.60
Purchase #6	$248.57	12.736%	$280.2279	$280.23	$280.25	$280.20
Purchase #7	$75.80	12.303%	$85.1257	$85.13	$85.15	$85.10
7 purchase totals =	$815.00		$900.3246	$900.34	$900.40	$900.30