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	$88.41	10.707%	$97.8761	$97.88	$97.90	$97.90
Purchase #2	$44.30	3.538%	$45.8673	$45.87	$45.85	$45.90
Purchase #3	$247.55	11.873%	$276.9416	$276.94	$276.95	$276.90
Purchase #4	$131.73	12.353%	$148.0026	$148.00	$148.00	$148.00
Purchase #5	$137.61	9.694%	$150.9499	$150.95	$150.95	$150.90
Purchase #6	$188.31	6.382%	$200.3279	$200.33	$200.35	$200.30
Purchase #7	$47.63	7.746%	$51.3194	$51.32	$51.30	$51.30
7 purchase totals =	$885.54		$971.2848	$971.29	$971.30	$971.20