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	$236.57	8.623%	$256.9694	$256.97	$256.95	$257.00
Purchase #2	$152.40	6.526%	$162.3456	$162.35	$162.35	$162.30
Purchase #3	$212.98	7.661%	$229.2964	$229.30	$229.30	$229.30
Purchase #4	$96.81	7.295%	$103.8723	$103.87	$103.85	$103.90
Purchase #5	$213.51	9.780%	$234.3913	$234.39	$234.40	$234.40
Purchase #6	$203.86	9.546%	$223.3205	$223.32	$223.30	$223.30
Purchase #7	$84.56	5.544%	$89.248	$89.25	$89.25	$89.20
7 purchase totals =	$1,200.69		$1,299.4435	$1,299.45	$1,299.40	$1,299.40