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	$6.90	3.127%	$7.1158	$7.12	$7.10	$7.10
Purchase #2	$33.77	4.799%	$35.3906	$35.39	$35.40	$35.40
Purchase #3	$58.36	10.645%	$64.5724	$64.57	$64.55	$64.60
Purchase #4	$17.59	5.412%	$18.542	$18.54	$18.55	$18.50
Purchase #5	$95.47	4.615%	$99.8759	$99.88	$99.90	$99.90
Purchase #6	$44.47	12.515%	$50.0354	$50.04	$50.05	$50.00
Purchase #7	$98.54	3.137%	$101.6312	$101.63	$101.65	$101.60
7 purchase totals =	$355.10		$377.1633	$377.17	$377.20	$377.10