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	$115.59	13.314%	$130.9797	$130.98	$131.00	$131.00
Purchase #2	$104.61	5.433%	$110.2935	$110.29	$110.30	$110.30
Purchase #3	$93.74	7.573%	$100.8389	$100.84	$100.85	$100.80
Purchase #4	$210.58	6.302%	$223.8508	$223.85	$223.85	$223.90
Purchase #5	$174.60	12.721%	$196.8109	$196.81	$196.80	$196.80
Purchase #6	$69.32	6.524%	$73.8424	$73.84	$73.85	$73.80
Purchase #7	$36.93	9.809%	$40.5525	$40.55	$40.55	$40.60
7 purchase totals =	$805.37		$877.1687	$877.16	$877.20	$877.20