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	$139.76	12.272%	$156.9113	$156.91	$156.90	$156.90
Purchase #2	$90.57	8.686%	$98.4369	$98.44	$98.45	$98.40
Purchase #3	$116.72	9.755%	$128.106	$128.11	$128.10	$128.10
Purchase #4	$182.33	12.622%	$205.3437	$205.34	$205.35	$205.30
Purchase #5	$137.67	6.867%	$147.1238	$147.12	$147.10	$147.10
Purchase #6	$203.66	4.647%	$213.1241	$213.12	$213.10	$213.10
Purchase #7	$61.79	12.556%	$69.5484	$69.55	$69.55	$69.50
7 purchase totals =	$932.50		$1,018.5942	$1,018.59	$1,018.55	$1,018.40