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	$121.32	9.800%	$133.2094	$133.21	$133.20	$133.20
Purchase #2	$113.94	9.404%	$124.6549	$124.65	$124.65	$124.70
Purchase #3	$70.61	11.628%	$78.8205	$78.82	$78.80	$78.80
Purchase #4	$145.85	4.645%	$152.6247	$152.62	$152.60	$152.60
Purchase #5	$137.40	3.851%	$142.6913	$142.69	$142.70	$142.70
Purchase #6	$53.50	3.315%	$55.2735	$55.27	$55.25	$55.30
Purchase #7	$241.52	13.282%	$273.5987	$273.60	$273.60	$273.60
7 purchase totals =	$884.14		$960.8730	$960.86	$960.80	$960.90