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	$18.40	7.555%	$19.7901	$19.79	$19.80	$19.80
Purchase #2	$181.57	9.250%	$198.3652	$198.37	$198.35	$198.40
Purchase #3	$78.80	13.366%	$89.3324	$89.33	$89.35	$89.30
Purchase #4	$221.88	5.677%	$234.4761	$234.48	$234.50	$234.50
Purchase #5	$161.39	11.860%	$180.5309	$180.53	$180.55	$180.50
Purchase #6	$144.72	5.175%	$152.2093	$152.21	$152.20	$152.20
Purchase #7	$218.92	11.668%	$244.4636	$244.46	$244.45	$244.50
7 purchase totals =	$1,025.68		$1,119.1676	$1,119.17	$1,119.20	$1,119.20