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	$113.63	12.576%	$127.9201	$127.92	$127.90	$127.90
Purchase #2	$152.69	12.150%	$171.2418	$171.24	$171.25	$171.20
Purchase #3	$95.54	11.404%	$106.4354	$106.44	$106.45	$106.40
Purchase #4	$193.67	13.387%	$219.5966	$219.60	$219.60	$219.60
Purchase #5	$242.34	4.410%	$253.0272	$253.03	$253.05	$253.00
Purchase #6	$155.32	8.710%	$168.8484	$168.85	$168.85	$168.80
Purchase #7	$43.37	3.645%	$44.9508	$44.95	$44.95	$45.00
7 purchase totals =	$996.56		$1,092.0203	$1,092.03	$1,092.05	$1,091.90