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	$85.86	5.217%	$90.3393	$90.34	$90.35	$90.30
Purchase #2	$195.50	13.120%	$221.1496	$221.15	$221.15	$221.10
Purchase #3	$137.70	3.458%	$142.4617	$142.46	$142.45	$142.50
Purchase #4	$19.63	3.591%	$20.3349	$20.33	$20.35	$20.30
Purchase #5	$216.61	5.415%	$228.3394	$228.34	$228.35	$228.30
Purchase #6	$126.40	11.190%	$140.5442	$140.54	$140.55	$140.50
Purchase #7	$186.85	5.291%	$196.7362	$196.74	$196.75	$196.70
7 purchase totals =	$968.55		$1,039.9053	$1,039.90	$1,039.95	$1,039.70