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	$136.89	10.541%	$151.3196	$151.32	$151.30	$151.30
Purchase #2	$158.50	6.442%	$168.7106	$168.71	$168.70	$168.70
Purchase #3	$105.47	7.578%	$113.4625	$113.46	$113.45	$113.50
Purchase #4	$5.62	7.106%	$6.0194	$6.02	$6.00	$6.00
Purchase #5	$42.72	3.408%	$44.1759	$44.18	$44.20	$44.20
Purchase #6	$184.93	6.470%	$196.895	$196.90	$196.90	$196.90
Purchase #7	$165.56	3.499%	$171.3529	$171.35	$171.35	$171.40
7 purchase totals =	$799.69		$851.9359	$851.94	$851.90	$852.00