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	$78.49	4.199%	$81.7858	$81.79	$81.80	$81.80
Purchase #2	$152.68	10.373%	$168.5175	$168.52	$168.50	$168.50
Purchase #3	$219.96	13.460%	$249.5666	$249.57	$249.55	$249.60
Purchase #4	$92.38	4.154%	$96.2175	$96.22	$96.20	$96.20
Purchase #5	$185.89	9.319%	$203.2131	$203.21	$203.20	$203.20
Purchase #6	$84.78	7.112%	$90.8096	$90.81	$90.80	$90.80
Purchase #7	$39.63	4.452%	$41.3943	$41.39	$41.40	$41.40
7 purchase totals =	$853.81		$931.5044	$931.51	$931.45	$931.50