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	$250.38	8.580%	$271.8626	$271.86	$271.85	$271.90
Purchase #2	$150.54	12.538%	$169.4147	$169.41	$169.40	$169.40
Purchase #3	$76.33	8.128%	$82.5341	$82.53	$82.55	$82.50
Purchase #4	$193.79	11.650%	$216.3665	$216.37	$216.35	$216.40
Purchase #5	$232.48	11.286%	$258.7177	$258.72	$258.70	$258.70
Purchase #6	$88.39	11.809%	$98.828	$98.83	$98.85	$98.80
Purchase #7	$208.91	8.834%	$227.3651	$227.37	$227.35	$227.40
7 purchase totals =	$1,200.82		$1,325.0887	$1,325.09	$1,325.05	$1,325.10