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	$52.76	13.176%	$59.7117	$59.71	$59.70	$59.70
Purchase #2	$250.61	5.449%	$264.2657	$264.27	$264.25	$264.30
Purchase #3	$123.65	13.476%	$140.3131	$140.31	$140.30	$140.30
Purchase #4	$141.67	7.756%	$152.6579	$152.66	$152.65	$152.70
Purchase #5	$125.85	4.285%	$131.2427	$131.24	$131.25	$131.20
Purchase #6	$194.84	13.718%	$221.5682	$221.57	$221.55	$221.60
Purchase #7	$133.94	7.581%	$144.094	$144.09	$144.10	$144.10
7 purchase totals =	$1,023.32		$1,113.8533	$1,113.85	$1,113.80	$1,113.90