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	$231.50	8.390%	$250.9229	$250.92	$250.90	$250.90
Purchase #2	$184.64	6.407%	$196.4699	$196.47	$196.45	$196.50
Purchase #3	$247.33	9.415%	$270.6161	$270.62	$270.60	$270.60
Purchase #4	$53.34	6.474%	$56.7932	$56.79	$56.80	$56.80
Purchase #5	$28.37	12.382%	$31.8828	$31.88	$31.90	$31.90
Purchase #6	$120.60	9.210%	$131.7073	$131.71	$131.70	$131.70
Purchase #7	$84.38	3.291%	$87.1569	$87.16	$87.15	$87.20
7 purchase totals =	$950.16		$1,025.5491	$1,025.55	$1,025.50	$1,025.60