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	$51.33	12.200%	$57.5923	$57.59	$57.60	$57.60
Purchase #2	$169.49	11.754%	$189.4119	$189.41	$189.40	$189.40
Purchase #3	$135.57	8.321%	$146.8508	$146.85	$146.85	$146.90
Purchase #4	$218.48	4.653%	$228.6459	$228.65	$228.65	$228.60
Purchase #5	$72.77	13.361%	$82.4928	$82.49	$82.50	$82.50
Purchase #6	$10.37	9.836%	$11.39	$11.39	$11.40	$11.40
Purchase #7	$197.82	9.304%	$216.2252	$216.23	$216.25	$216.20
7 purchase totals =	$855.83		$932.6089	$932.61	$932.65	$932.60