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	$245.32	4.703%	$256.8574	$256.86	$256.85	$256.90
Purchase #2	$201.61	4.134%	$209.9446	$209.94	$209.95	$209.90
Purchase #3	$178.48	11.150%	$198.3805	$198.38	$198.40	$198.40
Purchase #4	$187.33	4.807%	$196.335	$196.34	$196.35	$196.30
Purchase #5	$181.63	8.703%	$197.4373	$197.44	$197.45	$197.40
Purchase #6	$142.27	8.852%	$154.8637	$154.86	$154.85	$154.90
Purchase #7	$69.57	12.118%	$78.0005	$78.00	$78.00	$78.00
7 purchase totals =	$1,206.21		$1,291.8190	$1,291.82	$1,291.85	$1,291.80