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	$12.31	11.427%	$13.7167	$13.72	$13.70	$13.70
Purchase #2	$39.92	7.422%	$42.8829	$42.88	$42.90	$42.90
Purchase #3	$196.36	13.319%	$222.5132	$222.51	$222.50	$222.50
Purchase #4	$169.34	7.651%	$182.2962	$182.30	$182.30	$182.30
Purchase #5	$229.72	13.660%	$261.0998	$261.10	$261.10	$261.10
Purchase #6	$108.29	11.501%	$120.7444	$120.74	$120.75	$120.70
Purchase #7	$195.31	10.236%	$215.3019	$215.30	$215.30	$215.30
7 purchase totals =	$951.25		$1,058.5551	$1,058.55	$1,058.55	$1,058.50