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	$135.40	3.319%	$139.8939	$139.89	$139.90	$139.90
Purchase #2	$61.51	10.409%	$67.9126	$67.91	$67.90	$67.90
Purchase #3	$86.46	3.557%	$89.5354	$89.54	$89.55	$89.50
Purchase #4	$58.91	8.473%	$63.9014	$63.90	$63.90	$63.90
Purchase #5	$129.80	4.610%	$135.7838	$135.78	$135.80	$135.80
Purchase #6	$84.96	7.284%	$91.1485	$91.15	$91.15	$91.10
Purchase #7	$83.50	11.181%	$92.8361	$92.84	$92.85	$92.80
7 purchase totals =	$640.54		$681.0117	$681.01	$681.05	$680.90