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	$67.79	7.424%	$72.8227	$72.82	$72.80	$72.80
Purchase #2	$189.97	3.449%	$196.5221	$196.52	$196.50	$196.50
Purchase #3	$58.86	9.687%	$64.5618	$64.56	$64.55	$64.60
Purchase #4	$104.41	8.688%	$113.4811	$113.48	$113.50	$113.50
Purchase #5	$6.64	9.859%	$7.2946	$7.29	$7.30	$7.30
Purchase #6	$142.95	12.372%	$160.6358	$160.64	$160.65	$160.60
Purchase #7	$213.93	11.699%	$238.9577	$238.96	$238.95	$239.00
7 purchase totals =	$784.55		$854.2758	$854.27	$854.25	$854.30