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	$210.88	8.367%	$228.5243	$228.52	$228.50	$228.50
Purchase #2	$74.26	5.322%	$78.2121	$78.21	$78.20	$78.20
Purchase #3	$243.34	7.408%	$261.3666	$261.37	$261.35	$261.40
Purchase #4	$203.61	9.436%	$222.8226	$222.82	$222.80	$222.80
Purchase #5	$133.85	7.678%	$144.127	$144.13	$144.15	$144.10
Purchase #6	$45.86	12.224%	$51.4659	$51.47	$51.45	$51.50
Purchase #7	$245.39	9.359%	$268.3561	$268.36	$268.35	$268.40
7 purchase totals =	$1,157.19		$1,254.8746	$1,254.88	$1,254.80	$1,254.90