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	$246.54	10.805%	$273.1786	$273.18	$273.20	$273.20
Purchase #2	$229.36	12.708%	$258.5071	$258.51	$258.50	$258.50
Purchase #3	$95.47	5.310%	$100.5395	$100.54	$100.55	$100.50
Purchase #4	$80.68	10.869%	$89.4491	$89.45	$89.45	$89.40
Purchase #5	$25.53	9.228%	$27.8859	$27.89	$27.90	$27.90
Purchase #6	$167.86	7.790%	$180.9363	$180.94	$180.95	$180.90
Purchase #7	$69.38	9.851%	$76.2146	$76.21	$76.20	$76.20
7 purchase totals =	$914.82		$1,006.7111	$1,006.72	$1,006.75	$1,006.60