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	$22.37	12.780%	$25.2289	$25.23	$25.25	$25.20
Purchase #2	$96.29	3.739%	$99.8903	$99.89	$99.90	$99.90
Purchase #3	$78.67	6.656%	$83.9063	$83.91	$83.90	$83.90
Purchase #4	$54.73	9.311%	$59.8259	$59.83	$59.85	$59.80
Purchase #5	$92.96	3.825%	$96.5157	$96.52	$96.50	$96.50
Purchase #6	$224.67	7.405%	$241.3068	$241.31	$241.30	$241.30
Purchase #7	$41.76	3.837%	$43.3623	$43.36	$43.35	$43.40
7 purchase totals =	$611.45		$650.0362	$650.05	$650.05	$650.00