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	$180.57	6.773%	$192.8	$192.80	$192.80	$192.80
Purchase #2	$249.93	7.304%	$268.1849	$268.18	$268.20	$268.20
Purchase #3	$141.37	6.320%	$150.3046	$150.30	$150.30	$150.30
Purchase #4	$31.44	11.359%	$35.0113	$35.01	$35.00	$35.00
Purchase #5	$27.63	5.850%	$29.2464	$29.25	$29.25	$29.20
Purchase #6	$228.61	11.785%	$255.5517	$255.55	$255.55	$255.60
Purchase #7	$63.93	13.119%	$72.317	$72.32	$72.30	$72.30
7 purchase totals =	$923.48		$1,003.4159	$1,003.41	$1,003.40	$1,003.40