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	$189.52	13.619%	$215.3307	$215.33	$215.35	$215.30
Purchase #2	$147.81	7.498%	$158.8928	$158.89	$158.90	$158.90
Purchase #3	$87.44	13.636%	$99.3633	$99.36	$99.35	$99.40
Purchase #4	$61.28	10.402%	$67.6543	$67.65	$67.65	$67.70
Purchase #5	$106.41	3.594%	$110.2344	$110.23	$110.25	$110.20
Purchase #6	$68.83	3.272%	$71.0821	$71.08	$71.10	$71.10
Purchase #7	$40.51	5.298%	$42.6562	$42.66	$42.65	$42.70
7 purchase totals =	$701.80		$765.2138	$765.20	$765.25	$765.30