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	$187.59	13.396%	$212.7196	$212.72	$212.70	$212.70
Purchase #2	$87.59	5.618%	$92.5108	$92.51	$92.50	$92.50
Purchase #3	$17.56	6.537%	$18.7079	$18.71	$18.70	$18.70
Purchase #4	$131.71	7.786%	$141.9649	$141.96	$141.95	$142.00
Purchase #5	$77.43	8.206%	$83.7839	$83.78	$83.80	$83.80
Purchase #6	$153.31	12.112%	$171.8789	$171.88	$171.90	$171.90
Purchase #7	$171.50	5.755%	$181.3698	$181.37	$181.35	$181.40
7 purchase totals =	$826.69		$902.9358	$902.93	$902.90	$903.00