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	$181.89	10.319%	$200.6592	$200.66	$200.65	$200.70
Purchase #2	$153.61	13.542%	$174.4119	$174.41	$174.40	$174.40
Purchase #3	$167.54	13.433%	$190.0456	$190.05	$190.05	$190.00
Purchase #4	$59.35	11.755%	$66.3266	$66.33	$66.35	$66.30
Purchase #5	$24.54	12.355%	$27.5719	$27.57	$27.55	$27.60
Purchase #6	$40.56	4.458%	$42.3682	$42.37	$42.35	$42.40
Purchase #7	$217.34	11.607%	$242.5667	$242.57	$242.55	$242.60
7 purchase totals =	$844.83		$943.9501	$943.96	$943.90	$944.00