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	$68.47	3.868%	$71.1184	$71.12	$71.10	$71.10
Purchase #2	$169.88	5.322%	$178.921	$178.92	$178.90	$178.90
Purchase #3	$103.40	7.681%	$111.3422	$111.34	$111.35	$111.30
Purchase #4	$141.46	7.270%	$151.7441	$151.74	$151.75	$151.70
Purchase #5	$84.53	3.764%	$87.7117	$87.71	$87.70	$87.70
Purchase #6	$128.56	6.363%	$136.7403	$136.74	$136.75	$136.70
Purchase #7	$94.86	7.374%	$101.855	$101.86	$101.85	$101.90
7 purchase totals =	$791.16		$839.4327	$839.43	$839.40	$839.30