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	$79.79	12.625%	$89.8635	$89.86	$89.85	$89.90
Purchase #2	$33.30	6.254%	$35.3826	$35.38	$35.40	$35.40
Purchase #3	$125.83	5.203%	$132.3769	$132.38	$132.40	$132.40
Purchase #4	$250.33	5.258%	$263.4924	$263.49	$263.50	$263.50
Purchase #5	$34.63	6.542%	$36.8955	$36.90	$36.90	$36.90
Purchase #6	$215.71	12.746%	$243.2044	$243.20	$243.20	$243.20
Purchase #7	$60.25	7.215%	$64.597	$64.60	$64.60	$64.60
7 purchase totals =	$799.84		$865.8123	$865.81	$865.85	$865.90