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	$240.68	11.708%	$268.8588	$268.86	$268.85	$268.90
Purchase #2	$97.77	12.216%	$109.7136	$109.71	$109.70	$109.70
Purchase #3	$218.64	4.807%	$229.15	$229.15	$229.15	$229.20
Purchase #4	$250.93	7.604%	$270.0107	$270.01	$270.00	$270.00
Purchase #5	$32.76	13.667%	$37.2373	$37.24	$37.25	$37.20
Purchase #6	$207.82	13.820%	$236.5407	$236.54	$236.55	$236.50
Purchase #7	$89.45	11.666%	$99.8852	$99.89	$99.90	$99.90
7 purchase totals =	$1,138.05		$1,251.3963	$1,251.40	$1,251.40	$1,251.40