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	$45.31	13.577%	$51.4617	$51.46	$51.45	$51.50
Purchase #2	$155.48	8.620%	$168.8824	$168.88	$168.90	$168.90
Purchase #3	$114.63	4.364%	$119.6325	$119.63	$119.65	$119.60
Purchase #4	$196.34	5.862%	$207.8495	$207.85	$207.85	$207.80
Purchase #5	$154.97	7.800%	$167.0577	$167.06	$167.05	$167.10
Purchase #6	$234.49	3.701%	$243.1685	$243.17	$243.15	$243.20
Purchase #7	$154.37	9.760%	$169.4365	$169.44	$169.45	$169.40
7 purchase totals =	$1,055.59		$1,127.4888	$1,127.49	$1,127.50	$1,127.50