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	$76.81	7.148%	$82.3004	$82.30	$82.30	$82.30
Purchase #2	$51.39	10.684%	$56.8805	$56.88	$56.90	$56.90
Purchase #3	$39.46	12.695%	$44.4694	$44.47	$44.45	$44.50
Purchase #4	$89.45	10.449%	$98.7966	$98.80	$98.80	$98.80
Purchase #5	$175.39	5.731%	$185.4416	$185.44	$185.45	$185.40
Purchase #6	$171.42	6.735%	$182.9651	$182.97	$182.95	$183.00
Purchase #7	$11.97	7.620%	$12.8821	$12.88	$12.90	$12.90
7 purchase totals =	$615.89		$663.7357	$663.74	$663.75	$663.80