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	$37.81	12.825%	$42.6591	$42.66	$42.65	$42.70
Purchase #2	$211.25	9.478%	$231.2723	$231.27	$231.25	$231.30
Purchase #3	$99.97	9.718%	$109.6851	$109.69	$109.70	$109.70
Purchase #4	$98.73	13.737%	$112.2925	$112.29	$112.30	$112.30
Purchase #5	$106.97	13.801%	$121.7329	$121.73	$121.75	$121.70
Purchase #6	$241.79	13.281%	$273.9021	$273.90	$273.90	$273.90
Purchase #7	$94.44	11.558%	$105.3554	$105.36	$105.35	$105.40
7 purchase totals =	$890.96		$996.8994	$996.90	$996.90	$997.00