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	$174.65	3.387%	$180.5654	$180.57	$180.55	$180.60
Purchase #2	$78.93	12.764%	$89.0046	$89.00	$89.00	$89.00
Purchase #3	$42.39	7.151%	$45.4213	$45.42	$45.40	$45.40
Purchase #4	$238.49	11.434%	$265.7589	$265.76	$265.75	$265.80
Purchase #5	$86.65	8.362%	$93.8957	$93.90	$93.90	$93.90
Purchase #6	$106.36	6.575%	$113.3532	$113.35	$113.35	$113.40
Purchase #7	$133.89	5.198%	$140.8496	$140.85	$140.85	$140.80
7 purchase totals =	$861.36		$928.8487	$928.85	$928.80	$928.90