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	$148.67	13.265%	$168.3911	$168.39	$168.40	$168.40
Purchase #2	$37.94	11.258%	$42.2113	$42.21	$42.20	$42.20
Purchase #3	$204.25	3.257%	$210.9024	$210.90	$210.90	$210.90
Purchase #4	$86.61	11.871%	$96.8915	$96.89	$96.90	$96.90
Purchase #5	$58.67	13.423%	$66.5453	$66.55	$66.55	$66.50
Purchase #6	$243.77	7.208%	$261.3409	$261.34	$261.35	$261.30
Purchase #7	$80.97	10.511%	$89.4808	$89.48	$89.50	$89.50
7 purchase totals =	$860.88		$935.7633	$935.76	$935.80	$935.70