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	$29.31	3.379%	$30.3004	$30.30	$30.30	$30.30
Purchase #2	$98.54	11.554%	$109.9253	$109.93	$109.95	$109.90
Purchase #3	$73.73	3.163%	$76.0621	$76.06	$76.05	$76.10
Purchase #4	$84.67	6.179%	$89.9018	$89.90	$89.90	$89.90
Purchase #5	$176.49	13.590%	$200.475	$200.48	$200.50	$200.50
Purchase #6	$190.50	12.190%	$213.722	$213.72	$213.70	$213.70
Purchase #7	$244.80	9.271%	$267.4954	$267.50	$267.50	$267.50
7 purchase totals =	$898.04		$987.8820	$987.89	$987.90	$987.90