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	$131.71	6.827%	$140.7018	$140.70	$140.70	$140.70
Purchase #2	$233.40	6.789%	$249.2455	$249.25	$249.25	$249.20
Purchase #3	$56.76	5.505%	$59.8846	$59.88	$59.90	$59.90
Purchase #4	$109.73	12.474%	$123.4177	$123.42	$123.40	$123.40
Purchase #5	$223.55	3.867%	$232.1947	$232.19	$232.20	$232.20
Purchase #6	$208.96	10.648%	$231.2101	$231.21	$231.20	$231.20
Purchase #7	$42.37	5.855%	$44.8508	$44.85	$44.85	$44.90
7 purchase totals =	$1,006.48		$1,081.5052	$1,081.50	$1,081.50	$1,081.50