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	$127.83	10.555%	$141.3225	$141.32	$141.30	$141.30
Purchase #2	$128.47	8.576%	$139.4876	$139.49	$139.50	$139.50
Purchase #3	$250.29	8.419%	$271.3619	$271.36	$271.35	$271.40
Purchase #4	$228.36	5.489%	$240.8947	$240.89	$240.90	$240.90
Purchase #5	$50.54	3.528%	$52.3231	$52.32	$52.30	$52.30
Purchase #6	$163.34	9.778%	$179.3114	$179.31	$179.30	$179.30
Purchase #7	$91.97	3.744%	$95.4134	$95.41	$95.40	$95.40
7 purchase totals =	$1,040.80		$1,120.1146	$1,120.10	$1,120.05	$1,120.10