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	$180.55	3.296%	$186.5009	$186.50	$186.50	$186.50
Purchase #2	$167.61	8.641%	$182.0932	$182.09	$182.10	$182.10
Purchase #3	$240.93	13.547%	$273.5688	$273.57	$273.55	$273.60
Purchase #4	$207.43	13.239%	$234.8917	$234.89	$234.90	$234.90
Purchase #5	$62.84	7.832%	$67.7616	$67.76	$67.75	$67.80
Purchase #6	$7.43	6.381%	$7.9041	$7.90	$7.90	$7.90
Purchase #7	$89.41	12.759%	$100.8178	$100.82	$100.80	$100.80
7 purchase totals =	$956.20		$1,053.5381	$1,053.53	$1,053.50	$1,053.60