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	$7.98	4.190%	$8.3144	$8.31	$8.30	$8.30
Purchase #2	$5.54	4.796%	$5.8057	$5.81	$5.80	$5.80
Purchase #3	$170.53	11.657%	$190.4087	$190.41	$190.40	$190.40
Purchase #4	$72.59	12.780%	$81.867	$81.87	$81.85	$81.90
Purchase #5	$153.77	9.266%	$168.0183	$168.02	$168.00	$168.00
Purchase #6	$180.32	9.153%	$196.8247	$196.82	$196.80	$196.80
Purchase #7	$14.39	3.310%	$14.8663	$14.87	$14.85	$14.90
7 purchase totals =	$605.12		$666.1051	$666.11	$666.00	$666.10