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	$31.57	8.751%	$34.3327	$34.33	$34.35	$34.30
Purchase #2	$84.30	3.675%	$87.398	$87.40	$87.40	$87.40
Purchase #3	$92.36	6.249%	$98.1316	$98.13	$98.15	$98.10
Purchase #4	$53.78	4.527%	$56.2146	$56.21	$56.20	$56.20
Purchase #5	$43.79	3.872%	$45.4855	$45.49	$45.50	$45.50
Purchase #6	$69.73	4.196%	$72.6559	$72.66	$72.65	$72.70
Purchase #7	$165.45	12.355%	$185.8913	$185.89	$185.90	$185.90
7 purchase totals =	$540.98		$580.1096	$580.11	$580.15	$580.10