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	$111.27	10.721%	$123.1993	$123.20	$123.20	$123.20
Purchase #2	$242.94	5.191%	$255.551	$255.55	$255.55	$255.60
Purchase #3	$231.81	7.424%	$249.0196	$249.02	$249.00	$249.00
Purchase #4	$115.70	13.386%	$131.1876	$131.19	$131.20	$131.20
Purchase #5	$174.67	4.384%	$182.3275	$182.33	$182.35	$182.30
Purchase #6	$232.82	5.216%	$244.9639	$244.96	$244.95	$245.00
Purchase #7	$139.38	11.629%	$155.5885	$155.59	$155.60	$155.60
7 purchase totals =	$1,248.59		$1,341.8374	$1,341.84	$1,341.85	$1,341.90