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	$91.55	12.529%	$103.0203	$103.02	$103.00	$103.00
Purchase #2	$136.35	8.377%	$147.772	$147.77	$147.75	$147.80
Purchase #3	$141.69	5.746%	$149.8315	$149.83	$149.85	$149.80
Purchase #4	$69.53	3.122%	$71.7007	$71.70	$71.70	$71.70
Purchase #5	$29.53	10.289%	$32.5683	$32.57	$32.55	$32.60
Purchase #6	$66.96	12.700%	$75.4639	$75.46	$75.45	$75.50
Purchase #7	$179.75	9.123%	$196.1486	$196.15	$196.15	$196.10
7 purchase totals =	$715.36		$776.5053	$776.50	$776.45	$776.50