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	$99.82	3.527%	$103.3407	$103.34	$103.35	$103.30
Purchase #2	$127.43	9.333%	$139.323	$139.32	$139.30	$139.30
Purchase #3	$244.56	5.631%	$258.3312	$258.33	$258.35	$258.30
Purchase #4	$6.25	11.369%	$6.9606	$6.96	$6.95	$7.00
Purchase #5	$250.33	7.695%	$269.5929	$269.59	$269.60	$269.60
Purchase #6	$170.98	6.574%	$182.2202	$182.22	$182.20	$182.20
Purchase #7	$67.40	3.215%	$69.5669	$69.57	$69.55	$69.60
7 purchase totals =	$966.77		$1,029.3355	$1,029.33	$1,029.30	$1,029.30