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	$28.30	12.770%	$31.9139	$31.91	$31.90	$31.90
Purchase #2	$190.82	9.459%	$208.8697	$208.87	$208.85	$208.90
Purchase #3	$228.76	5.122%	$240.4771	$240.48	$240.50	$240.50
Purchase #4	$153.96	11.651%	$171.8979	$171.90	$171.90	$171.90
Purchase #5	$135.40	8.435%	$146.821	$146.82	$146.80	$146.80
Purchase #6	$85.65	12.508%	$96.3631	$96.36	$96.35	$96.40
Purchase #7	$83.64	6.509%	$89.0841	$89.08	$89.10	$89.10
7 purchase totals =	$906.53		$985.4268	$985.42	$985.40	$985.50