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	$88.78	11.520%	$99.0075	$99.01	$99.00	$99.00
Purchase #2	$138.90	12.697%	$156.5361	$156.54	$156.55	$156.50
Purchase #3	$78.86	8.619%	$85.6569	$85.66	$85.65	$85.70
Purchase #4	$200.39	7.736%	$215.8922	$215.89	$215.90	$215.90
Purchase #5	$193.78	13.762%	$220.448	$220.45	$220.45	$220.40
Purchase #6	$110.90	13.191%	$125.5288	$125.53	$125.55	$125.50
Purchase #7	$170.40	6.693%	$181.8049	$181.80	$181.80	$181.80
7 purchase totals =	$982.01		$1,084.8744	$1,084.88	$1,084.90	$1,084.80