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	$95.63	4.783%	$100.204	$100.20	$100.20	$100.20
Purchase #2	$164.32	12.725%	$185.2297	$185.23	$185.25	$185.20
Purchase #3	$224.86	9.855%	$247.02	$247.02	$247.00	$247.00
Purchase #4	$171.48	10.731%	$189.8815	$189.88	$189.90	$189.90
Purchase #5	$168.65	7.844%	$181.8789	$181.88	$181.90	$181.90
Purchase #6	$36.53	12.672%	$41.1591	$41.16	$41.15	$41.20
Purchase #7	$141.33	9.818%	$155.2058	$155.21	$155.20	$155.20
7 purchase totals =	$1,002.80		$1,100.5790	$1,100.58	$1,100.60	$1,100.60