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	$49.48	3.225%	$51.0757	$51.08	$51.10	$51.10
Purchase #2	$219.84	6.845%	$234.888	$234.89	$234.90	$234.90
Purchase #3	$7.47	9.447%	$8.1757	$8.18	$8.20	$8.20
Purchase #4	$179.56	6.629%	$191.463	$191.46	$191.45	$191.50
Purchase #5	$178.74	6.515%	$190.3849	$190.38	$190.40	$190.40
Purchase #6	$167.80	12.732%	$189.1643	$189.16	$189.15	$189.20
Purchase #7	$155.31	6.165%	$164.8849	$164.88	$164.90	$164.90
7 purchase totals =	$958.20		$1,030.0365	$1,030.03	$1,030.10	$1,030.20