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	$135.83	3.356%	$140.3885	$140.39	$140.40	$140.40
Purchase #2	$159.75	5.500%	$168.5363	$168.54	$168.55	$168.50
Purchase #3	$95.89	8.835%	$104.3619	$104.36	$104.35	$104.40
Purchase #4	$150.66	5.348%	$158.7173	$158.72	$158.70	$158.70
Purchase #5	$142.55	9.253%	$155.7402	$155.74	$155.75	$155.70
Purchase #6	$146.88	6.812%	$156.8855	$156.89	$156.90	$156.90
Purchase #7	$121.59	3.290%	$125.5903	$125.59	$125.60	$125.60
7 purchase totals =	$953.15		$1,010.2200	$1,010.23	$1,010.25	$1,010.20