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	$5.40	3.506%	$5.5893	$5.59	$5.60	$5.60
Purchase #2	$203.83	11.741%	$227.7617	$227.76	$227.75	$227.80
Purchase #3	$231.44	9.569%	$253.5865	$253.59	$253.60	$253.60
Purchase #4	$51.72	3.134%	$53.3409	$53.34	$53.35	$53.30
Purchase #5	$196.49	8.841%	$213.8617	$213.86	$213.85	$213.90
Purchase #6	$165.59	12.192%	$185.7787	$185.78	$185.80	$185.80
Purchase #7	$202.36	8.666%	$219.8965	$219.90	$219.90	$219.90
7 purchase totals =	$1,056.83		$1,159.8153	$1,159.82	$1,159.85	$1,159.90