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	$98.32	3.585%	$101.8448	$101.84	$101.85	$101.80
Purchase #2	$151.29	13.625%	$171.9033	$171.90	$171.90	$171.90
Purchase #3	$171.81	12.281%	$192.91	$192.91	$192.90	$192.90
Purchase #4	$152.43	12.250%	$171.1027	$171.10	$171.10	$171.10
Purchase #5	$194.89	11.508%	$217.3179	$217.32	$217.30	$217.30
Purchase #6	$114.88	3.778%	$119.2202	$119.22	$119.20	$119.20
Purchase #7	$250.93	13.796%	$285.5483	$285.55	$285.55	$285.50
7 purchase totals =	$1,134.55		$1,259.8472	$1,259.84	$1,259.80	$1,259.70