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	$211.57	12.834%	$238.7229	$238.72	$238.70	$238.70
Purchase #2	$56.89	5.215%	$59.8568	$59.86	$59.85	$59.90
Purchase #3	$230.82	6.283%	$245.3224	$245.32	$245.30	$245.30
Purchase #4	$196.94	9.639%	$215.923	$215.92	$215.90	$215.90
Purchase #5	$27.98	9.321%	$30.588	$30.59	$30.60	$30.60
Purchase #6	$7.88	3.134%	$8.127	$8.13	$8.15	$8.10
Purchase #7	$29.79	4.299%	$31.0707	$31.07	$31.05	$31.10
7 purchase totals =	$761.87		$829.6108	$829.61	$829.55	$829.60