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	$58.37	11.520%	$65.0942	$65.09	$65.10	$65.10
Purchase #2	$48.25	12.204%	$54.1384	$54.14	$54.15	$54.10
Purchase #3	$20.84	3.148%	$21.496	$21.50	$21.50	$21.50
Purchase #4	$57.43	11.262%	$63.8978	$63.90	$63.90	$63.90
Purchase #5	$195.41	9.294%	$213.5714	$213.57	$213.55	$213.60
Purchase #6	$168.69	6.637%	$179.886	$179.89	$179.90	$179.90
Purchase #7	$43.99	8.868%	$47.891	$47.89	$47.90	$47.90
7 purchase totals =	$592.98		$645.9748	$645.98	$646.00	$646.00