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	$94.34	9.533%	$103.3334	$103.33	$103.35	$103.30
Purchase #2	$59.91	9.307%	$65.4858	$65.49	$65.50	$65.50
Purchase #3	$202.36	10.642%	$223.8952	$223.90	$223.90	$223.90
Purchase #4	$118.90	11.849%	$132.9885	$132.99	$133.00	$133.00
Purchase #5	$140.25	7.263%	$150.4364	$150.44	$150.45	$150.40
Purchase #6	$78.70	4.788%	$82.4682	$82.47	$82.45	$82.50
Purchase #7	$140.91	4.632%	$147.437	$147.44	$147.45	$147.40
7 purchase totals =	$835.37		$906.0445	$906.06	$906.10	$906.00