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	$56.41	12.661%	$63.5521	$63.55	$63.55	$63.60
Purchase #2	$218.49	12.460%	$245.7139	$245.71	$245.70	$245.70
Purchase #3	$164.69	11.253%	$183.2226	$183.22	$183.20	$183.20
Purchase #4	$213.81	12.488%	$240.5106	$240.51	$240.50	$240.50
Purchase #5	$137.54	10.178%	$151.5388	$151.54	$151.55	$151.50
Purchase #6	$45.36	3.311%	$46.8619	$46.86	$46.85	$46.90
Purchase #7	$73.66	6.148%	$78.1886	$78.19	$78.20	$78.20
7 purchase totals =	$909.96		$1,009.5885	$1,009.58	$1,009.55	$1,009.60