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	$6.35	5.196%	$6.6799	$6.68	$6.70	$6.70
Purchase #2	$89.58	7.853%	$96.6147	$96.61	$96.60	$96.60
Purchase #3	$189.71	9.647%	$208.0113	$208.01	$208.00	$208.00
Purchase #4	$233.77	13.177%	$264.5739	$264.57	$264.55	$264.60
Purchase #5	$56.96	5.119%	$59.8758	$59.88	$59.90	$59.90
Purchase #6	$109.39	13.746%	$124.4267	$124.43	$124.45	$124.40
Purchase #7	$232.56	12.516%	$261.6672	$261.67	$261.65	$261.70
7 purchase totals =	$918.32		$1,021.8495	$1,021.85	$1,021.85	$1,021.90