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	$240.65	4.134%	$250.5985	$250.60	$250.60	$250.60
Purchase #2	$155.47	5.658%	$164.2665	$164.27	$164.25	$164.30
Purchase #3	$90.55	12.299%	$101.6867	$101.69	$101.70	$101.70
Purchase #4	$166.34	7.796%	$179.3079	$179.31	$179.30	$179.30
Purchase #5	$164.53	12.111%	$184.4562	$184.46	$184.45	$184.50
Purchase #6	$157.92	11.712%	$176.4156	$176.42	$176.40	$176.40
Purchase #7	$68.67	13.790%	$78.1396	$78.14	$78.15	$78.10
7 purchase totals =	$1,044.13		$1,134.8710	$1,134.89	$1,134.85	$1,134.90