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	$39.69	6.610%	$42.3135	$42.31	$42.30	$42.30
Purchase #2	$191.28	10.264%	$210.913	$210.91	$210.90	$210.90
Purchase #3	$123.84	12.730%	$139.6048	$139.60	$139.60	$139.60
Purchase #4	$126.36	12.310%	$141.9149	$141.91	$141.90	$141.90
Purchase #5	$196.42	12.805%	$221.5716	$221.57	$221.55	$221.60
Purchase #6	$224.34	10.175%	$247.1666	$247.17	$247.15	$247.20
Purchase #7	$63.60	9.755%	$69.8042	$69.80	$69.80	$69.80
7 purchase totals =	$965.53		$1,073.2886	$1,073.27	$1,073.20	$1,073.30