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	$19.96	13.294%	$22.6135	$22.61	$22.60	$22.60
Purchase #2	$70.73	13.591%	$80.3429	$80.34	$80.35	$80.30
Purchase #3	$203.76	7.112%	$218.2514	$218.25	$218.25	$218.30
Purchase #4	$73.75	12.401%	$82.8957	$82.90	$82.90	$82.90
Purchase #5	$41.56	4.654%	$43.4942	$43.49	$43.50	$43.50
Purchase #6	$190.37	10.541%	$210.4369	$210.44	$210.45	$210.40
Purchase #7	$65.89	7.501%	$70.8324	$70.83	$70.85	$70.80
7 purchase totals =	$666.02		$728.8670	$728.86	$728.90	$728.80