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	$135.71	5.280%	$142.8755	$142.88	$142.90	$142.90
Purchase #2	$150.31	9.689%	$164.8735	$164.87	$164.85	$164.90
Purchase #3	$221.86	12.255%	$249.0489	$249.05	$249.05	$249.00
Purchase #4	$75.66	9.493%	$82.8424	$82.84	$82.85	$82.80
Purchase #5	$250.87	9.557%	$274.8456	$274.85	$274.85	$274.80
Purchase #6	$109.59	9.402%	$119.8937	$119.89	$119.90	$119.90
Purchase #7	$27.71	12.646%	$31.2142	$31.21	$31.20	$31.20
7 purchase totals =	$971.71		$1,065.5938	$1,065.59	$1,065.60	$1,065.50