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	$209.29	6.819%	$223.5615	$223.56	$223.55	$223.60
Purchase #2	$136.40	10.395%	$150.5788	$150.58	$150.60	$150.60
Purchase #3	$133.89	12.695%	$150.8873	$150.89	$150.90	$150.90
Purchase #4	$63.55	11.473%	$70.8411	$70.84	$70.85	$70.80
Purchase #5	$228.46	6.705%	$243.7782	$243.78	$243.80	$243.80
Purchase #6	$228.55	6.129%	$242.5578	$242.56	$242.55	$242.60
Purchase #7	$98.27	6.713%	$104.8669	$104.87	$104.85	$104.90
7 purchase totals =	$1,098.41		$1,187.0716	$1,187.08	$1,187.10	$1,187.20