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	$150.56	6.179%	$159.8631	$159.86	$159.85	$159.90
Purchase #2	$245.68	10.843%	$272.3191	$272.32	$272.30	$272.30
Purchase #3	$109.25	13.738%	$124.2588	$124.26	$124.25	$124.30
Purchase #4	$42.91	3.329%	$44.3385	$44.34	$44.35	$44.30
Purchase #5	$29.48	6.536%	$31.4068	$31.41	$31.40	$31.40
Purchase #6	$97.67	12.468%	$109.8475	$109.85	$109.85	$109.80
Purchase #7	$242.98	7.788%	$261.9033	$261.90	$261.90	$261.90
7 purchase totals =	$918.53		$1,003.9371	$1,003.94	$1,003.90	$1,003.90