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	$250.66	11.775%	$280.1752	$280.18	$280.20	$280.20
Purchase #2	$142.34	3.351%	$147.1098	$147.11	$147.10	$147.10
Purchase #3	$122.72	7.119%	$131.4564	$131.46	$131.45	$131.50
Purchase #4	$50.71	6.505%	$54.0087	$54.01	$54.00	$54.00
Purchase #5	$129.56	8.468%	$140.5311	$140.53	$140.55	$140.50
Purchase #6	$234.88	6.620%	$250.4291	$250.43	$250.45	$250.40
Purchase #7	$126.97	3.860%	$131.871	$131.87	$131.85	$131.90
7 purchase totals =	$1,057.84		$1,135.5813	$1,135.59	$1,135.60	$1,135.60