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	$71.39	12.604%	$80.388	$80.39	$80.40	$80.40
Purchase #2	$45.91	3.108%	$47.3369	$47.34	$47.35	$47.30
Purchase #3	$85.39	4.155%	$88.938	$88.94	$88.95	$88.90
Purchase #4	$63.96	5.106%	$67.2258	$67.23	$67.25	$67.20
Purchase #5	$49.92	3.576%	$51.7051	$51.71	$51.70	$51.70
Purchase #6	$126.77	12.684%	$142.8495	$142.85	$142.85	$142.80
Purchase #7	$72.84	4.836%	$76.3625	$76.36	$76.35	$76.40
7 purchase totals =	$516.18		$554.8058	$554.82	$554.85	$554.70