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	$17.56	7.848%	$18.9381	$18.94	$18.95	$18.90
Purchase #2	$240.73	13.739%	$273.8039	$273.80	$273.80	$273.80
Purchase #3	$110.53	13.415%	$125.3576	$125.36	$125.35	$125.40
Purchase #4	$174.82	12.299%	$196.3211	$196.32	$196.30	$196.30
Purchase #5	$105.72	13.148%	$119.6201	$119.62	$119.60	$119.60
Purchase #6	$86.62	12.584%	$97.5203	$97.52	$97.50	$97.50
Purchase #7	$187.95	11.221%	$209.0399	$209.04	$209.05	$209.00
7 purchase totals =	$923.93		$1,040.6010	$1,040.60	$1,040.55	$1,040.50