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	$67.31	6.270%	$71.5303	$71.53	$71.55	$71.50
Purchase #2	$109.89	12.373%	$123.4867	$123.49	$123.50	$123.50
Purchase #3	$137.33	9.192%	$149.9534	$149.95	$149.95	$150.00
Purchase #4	$103.63	11.476%	$115.5226	$115.52	$115.50	$115.50
Purchase #5	$41.53	6.755%	$44.3354	$44.34	$44.35	$44.30
Purchase #6	$92.32	6.706%	$98.511	$98.51	$98.50	$98.50
Purchase #7	$218.76	13.324%	$247.9076	$247.91	$247.90	$247.90
7 purchase totals =	$770.77		$851.2470	$851.25	$851.25	$851.20