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	$18.36	11.415%	$20.4558	$20.46	$20.45	$20.50
Purchase #2	$75.30	13.193%	$85.2343	$85.23	$85.25	$85.20
Purchase #3	$150.29	9.496%	$164.5615	$164.56	$164.55	$164.60
Purchase #4	$200.84	7.132%	$215.1639	$215.16	$215.15	$215.20
Purchase #5	$83.81	5.494%	$88.4145	$88.41	$88.40	$88.40
Purchase #6	$46.47	7.679%	$50.0384	$50.04	$50.05	$50.00
Purchase #7	$164.72	6.824%	$175.9605	$175.96	$175.95	$176.00
7 purchase totals =	$739.79		$799.8289	$799.82	$799.80	$799.90