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	$29.89	12.107%	$33.5088	$33.51	$33.50	$33.50
Purchase #2	$211.57	13.872%	$240.919	$240.92	$240.90	$240.90
Purchase #3	$244.72	9.287%	$267.4471	$267.45	$267.45	$267.40
Purchase #4	$227.86	5.469%	$240.3217	$240.32	$240.30	$240.30
Purchase #5	$147.79	13.464%	$167.6884	$167.69	$167.70	$167.70
Purchase #6	$139.94	7.688%	$150.6986	$150.70	$150.70	$150.70
Purchase #7	$240.66	9.837%	$264.3337	$264.33	$264.35	$264.30
7 purchase totals =	$1,242.43		$1,364.9173	$1,364.92	$1,364.90	$1,364.80