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	$137.32	3.740%	$142.4558	$142.46	$142.45	$142.50
Purchase #2	$122.90	11.382%	$136.8885	$136.89	$136.90	$136.90
Purchase #3	$7.27	12.507%	$8.1793	$8.18	$8.20	$8.20
Purchase #4	$81.53	10.154%	$89.8086	$89.81	$89.80	$89.80
Purchase #5	$43.90	3.215%	$45.3114	$45.31	$45.30	$45.30
Purchase #6	$92.87	10.755%	$102.8582	$102.86	$102.85	$102.90
Purchase #7	$133.42	8.146%	$144.2884	$144.29	$144.30	$144.30
7 purchase totals =	$619.21		$669.7902	$669.80	$669.80	$669.90