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	$49.71	13.744%	$56.5421	$56.54	$56.55	$56.50
Purchase #2	$250.50	12.700%	$282.3135	$282.31	$282.30	$282.30
Purchase #3	$40.32	9.701%	$44.2314	$44.23	$44.25	$44.20
Purchase #4	$159.72	11.775%	$178.527	$178.53	$178.55	$178.50
Purchase #5	$27.96	11.751%	$31.2456	$31.25	$31.25	$31.20
Purchase #6	$6.72	5.705%	$7.1034	$7.10	$7.10	$7.10
Purchase #7	$136.71	7.473%	$146.9263	$146.93	$146.95	$146.90
7 purchase totals =	$671.64		$746.8893	$746.89	$746.95	$746.70