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	$61.50	10.309%	$67.84	$67.84	$67.85	$67.80
Purchase #2	$51.79	13.609%	$58.8381	$58.84	$58.85	$58.80
Purchase #3	$65.89	11.354%	$73.3712	$73.37	$73.35	$73.40
Purchase #4	$93.28	5.571%	$98.4766	$98.48	$98.50	$98.50
Purchase #5	$31.33	7.741%	$33.7553	$33.76	$33.75	$33.80
Purchase #6	$123.31	6.669%	$131.5335	$131.53	$131.55	$131.50
Purchase #7	$167.71	7.424%	$180.1608	$180.16	$180.15	$180.20
7 purchase totals =	$594.81		$643.9755	$643.98	$644.00	$644.00