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	$10.25	12.438%	$11.5249	$11.52	$11.50	$11.50
Purchase #2	$80.63	10.207%	$88.8599	$88.86	$88.85	$88.90
Purchase #3	$121.54	8.329%	$131.6631	$131.66	$131.65	$131.70
Purchase #4	$78.82	13.209%	$89.2313	$89.23	$89.25	$89.20
Purchase #5	$6.94	8.219%	$7.5104	$7.51	$7.50	$7.50
Purchase #6	$212.36	13.179%	$240.3469	$240.35	$240.35	$240.30
Purchase #7	$23.64	3.818%	$24.5426	$24.54	$24.55	$24.50
7 purchase totals =	$534.18		$593.6791	$593.67	$593.65	$593.60