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	$122.47	7.515%	$131.6736	$131.67	$131.65	$131.70
Purchase #2	$82.86	8.174%	$89.633	$89.63	$89.65	$89.60
Purchase #3	$144.25	13.765%	$164.106	$164.11	$164.10	$164.10
Purchase #4	$185.57	12.596%	$208.9444	$208.94	$208.95	$208.90
Purchase #5	$5.90	11.709%	$6.5908	$6.59	$6.60	$6.60
Purchase #6	$145.36	10.168%	$160.1402	$160.14	$160.15	$160.10
Purchase #7	$49.28	13.401%	$55.884	$55.88	$55.90	$55.90
7 purchase totals =	$735.69		$816.9720	$816.96	$817.00	$816.90