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	$6.78	5.401%	$7.1462	$7.15	$7.15	$7.10
Purchase #2	$218.58	11.410%	$243.52	$243.52	$243.50	$243.50
Purchase #3	$196.79	3.442%	$203.5635	$203.56	$203.55	$203.60
Purchase #4	$89.94	11.383%	$100.1779	$100.18	$100.20	$100.20
Purchase #5	$92.27	8.785%	$100.3759	$100.38	$100.40	$100.40
Purchase #6	$159.28	3.263%	$164.4773	$164.48	$164.50	$164.50
Purchase #7	$185.28	12.502%	$208.4437	$208.44	$208.45	$208.40
7 purchase totals =	$948.92		$1,027.7045	$1,027.71	$1,027.75	$1,027.70