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	$247.38	11.840%	$276.6698	$276.67	$276.65	$276.70
Purchase #2	$142.90	9.545%	$156.5398	$156.54	$156.55	$156.50
Purchase #3	$86.95	11.454%	$96.9093	$96.91	$96.90	$96.90
Purchase #4	$35.69	6.360%	$37.9599	$37.96	$37.95	$38.00
Purchase #5	$128.71	7.127%	$137.8832	$137.88	$137.90	$137.90
Purchase #6	$144.69	4.218%	$150.793	$150.79	$150.80	$150.80
Purchase #7	$138.77	9.803%	$152.3736	$152.37	$152.35	$152.40
7 purchase totals =	$925.09		$1,009.1286	$1,009.12	$1,009.10	$1,009.20